October 31st, 2013
10:45 AM ET
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Editor's Note: America's Test Kitchen is a real 2,500 square foot test kitchen located just outside of Boston that is home to more than three dozen full-time cooks and product testers. Our mission is simple: to develop the absolute best recipes for all of your favorite foods. To do this, we test each recipe 30, 40, sometimes as many as 70 times, until we arrive at the combination of ingredients, technique, temperature, cooking time, and equipment that yields the best, most-foolproof recipe. America’s Test Kitchen's online cooking school is based on nearly 20 years of test kitchen work in our own facility, on the recipes created for Cook’s Illustrated magazine, and on our two public television cooking shows.

A crumb crust is a classic choice in many single-crust pies. It’s more durable than classic pie dough, making it the right choice for the moist custard-based fillings in recipes like Key Lime Pie (recipe below).

Graham crackers are the classic choice. For chocolate cookie crusts, we prefer Oreos. While buying a store-bought ready-to-go crust is a tempting shortcut, these are always stale and bland. Making your own is incredibly easy and well worth it for a fresh-tasting crust with a crisp texture and balanced sweetness to do your homemade pie filling justice.

Essential Equipment
– Food processor
– 9-inch pie plate, preferably glass
– Dry measuring cup

1. Grind crumbs
Break 8 whole graham crackers or 16 sandwich cookies (such as chocolate or peanut butter sandwich cookies) into rough pieces and place in food processor. If using graham crackers, process to fine crumbs, about 30 seconds. For sandwich cookies, pulse until coarsely ground, then process to fine crumbs. Sprinkle sugar (if using) and melted, cooled butter over crumbs and pulse to incorporate, about 5 pulses.

Why? The metal blade of a food processor turns hard crackers or cookies into even crumbs in seconds. It’s also the best way to incorporate the sugar (a must with graham crackers, but unnecessary with sweeter cookies) and melted butter. Since sandwich cookies are heftier than graham crackers, it’s best to break them up before processing.

2. Shape into crust
Sprinkle crumb mixture into 9-inch pie plate. use bottom of dry measuring cup to press crumb mixture firmly and evenly across bottom of pie plate. Then tightly pack crumbs against side of pie plate using side of measuring cup.

Why? The butter moistens the crumbs, but a little elbow grease is required to create a cohesive crust. Make sure to build the crust up the sides of the pie plate. A dry measuring cup (the 1/3 or 1/2 cup measure in most sets works best) keeps your hands clean and allows you to create an even, firmly packed surface.

3. Bake until fragrant and just browning
Adjust oven rack to middle position and heat oven to 325 degrees. Bake until crust is fragrant and beginning to brown, 13 to 18 minutes. Use crust immediately or cool as directed in pie recipe.

Why? Many recipes skip the prebaking step, but this is a big mistake. Baking the crumbs makes the crust cohesive and gives mild graham crackers a nice toasty flavor.

Common Questions

Q: I want to use store-bought graham cracker crumbs.

A: In theory, these crumbs would work in our recipe, but we have found that they are often quite stale. And they don’t save you much time, since you still need to add sugar and melted butter. We strongly recommend you take 30 seconds to grind your own crumbs.

Q: Can I just use a store-bought graham cracker crust?

A: Please don’t! We tasted three leading brands and were shocked at their bland, artificial flavor and sandy, crumbly texture. Commercial crusts are made with shortening, not butter, and you can taste the difference. Also, these crusts aren’t sufficiently baked. The 5 minutes of hands-on work needed to make your own crumb crust is time well spent.

Q: I can’t tell if the crust is done baking.

A: While you can easily use color change to judge when pie dough is baked, it’s pretty difficult to tell when a crumb crust is done, at least with just your eyes. The crust should be fragrant (but not burned) and firm to the touch. If the crust feels soft or not quite set, give it a few more minutes in the oven.

Q: Can I use chocolate wafer cookies instead of Oreos for a chocolate crust?

A: We wouldn’t recommend it. Chocolate wafer cookies are the more conventional choice for this type of crust, but we have found that they taste bland and tough. Because of the richness of the Oreo filling, the crust is guaranteed to be tender.

Key Lime Pie
Source: America's Test Kitchen
Serves 8

Why this recipe works
Key lime pie often disappoints us with a harsh and artificial flavor. We wanted a recipe for classic Key lime pie with a fresh flavor and silky filling.

Traditional Key lime pie is usually not baked; instead, the combination of egg yolks, lime juice, and sweetened condensed milk firms up when chilled because the juice’s acidity causes the proteins in the eggs and milk to bind. We found that just one simple swap—from bottled, reconstituted lime juice to juice and zest from fresh limes—gave us a pie that was pungent and refreshing, cool yet creamy, and very satisfying.

We also discovered that while the pie filling will set without baking (most recipes call only for mixing and then chilling), it set much more nicely after being baked for only 15 minutes. We tried more dramatic departures from the “classic” recipe—folding in egg whites, substituting heavy cream for condensed milk—but they didn’t work. Just two seemingly minor adjustments to the classic recipe made all the difference.

Despite this pie’s name, we found that most tasters could not tell the difference between pies made with regular supermarket limes (called Persian limes) and true Key limes. Since Persian limes are easier to find and juice, we recommend them.

The timing here is different from other pies; you need to make the filling first, then prepare the crust. We don’t recommend using store-bought graham cracker crumbs here as they can often be stale.

4 large egg yolks
4 teaspoons grated lime zest plus 1/2 cup juice (5 limes)
1 (14-ounce) can sweetened condensed milk

Graham Cracker Crust
8 whole graham crackers, broken into 1-inch pieces
5 tablespoons unsalted butter, melted and cooled
3 tablespoons sugar

Topping (optional)
1 cup heavy cream, chilled
1/4 cup (1 ounce) confectioners’ sugar

1. FOR THE PIE: Whisk egg yolks and lime zest together in medium bowl until mixture has light green tint, about 2 minutes. Whisk in condensed milk until smooth, then whisk in lime juice. Cover mixture and set aside at room temperature until thickened, about 30 minutes.

2. Meanwhile, prepare and bake crust. Adjust oven rack to middle position and heat oven to 325 degrees. Process graham cracker pieces in food processor to fine, even crumbs, about 30 seconds. Sprinkle melted butter and sugar over crumbs and pulse to incorporate, about 5 pulses.

3. Sprinkle mixture into 9-inch pie plate. Using bottom of dry measuring cup, press crumbs into even layer on bottom and sides of pie plate. Bake until crust is fragrant and beginning to brown, 13 to 18 minutes; transfer to wire rack and leave oven at 325 degrees. (Crust must still be warm when filling is added.)

4. Pour thickened filling into warm prebaked pie crust. Bake pie until center is firm but jiggles slightly when shaken, 15 to 20 minutes. Let pie cool slightly on wire rack, about 1 hour, then cover loosely with plastic wrap and refrigerate until filling is chilled and set, about 3 hours.

5. FOR THE TOPPING, IF USING: Once pie is chilled, use stand mixer fitted with whisk to whip cream and sugar on medium-low speed until foamy, about 1 minute. Increase speed to high and whip until soft peaks form, 1 to 3 minutes. Spread whipped cream attractively over top of pie. Serve.

This pie tutorial and recipe are from the America's Test Kitchen Cooking School Cookbook. With 832 pages, 600 recipes, and 2,500 photos, it has everything you need to become a great cook.

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Filed under: America's Test Kitchen • Baked Goods • Content Partner • How To • Make • Pie • Recipes • Techniques & Tips

soundoff (9 Responses)
  1. Carol H

    key limes should be yellow not green when you use them. I have lived in Florida all my life and have a key lime tree.
    Stores sell key limes when there green and people don't know they should be yellow. The juice is biter when there still green.

    October 20, 2014 at 4:13 pm |
    • I

      had no idea.

      October 21, 2014 at 8:21 am |
  2. Vivienne Faulknen

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    January 14, 2014 at 7:13 am |
  3. Kathleen

    Is this recipe telling me to use the ENTIRE Oreo, filling and all? Not just the cookie part? I'd think that cream filling wouldn't do so well–a lumpy bunch of crumbs and no telling what the oven might do to it.

    Has anyone else tried this? Does it work?

    October 31, 2013 at 2:57 pm |
    • yoyo1198

      Yes. Grind wafer plus filling. You won't get a bunch of lumps. The food processor will do its job.

      November 4, 2013 at 2:22 pm |
  4. Cook In / Dine Out

    This is a great story. I recently made a pie with a crumb crust (apple custard pie with gingersnap crust) and was on the fence about pre-baking the crust. I decided not to, since I was concerned it would make it too hard, but in retrospect, it might have been nice to give the crust a little more structure by doing so. One issue I had was that the top edge of the crust that extended above the filling got a little burnt in places. Any recommendations for dealing with that? The filling was really good, so I don't think I overbaked the pie.

    October 31, 2013 at 12:18 pm |
    • Michelle

      To Cook In/Dine Out – My mother always covers just the edge of the crust with aluminum foil when baking to prevent burning it and it seems to work well for her.

      October 31, 2013 at 4:03 pm |
    • Leah

      Cover the edge with foil but take off the foil for the last few minutes of baking. This will ensure the edges don't get burnt but the rest of the pie still cooks. It works for any kind of pie, like apple or fruit pies that need to be baked a while to set the filling, but run the risk of burnt edges due to the long baking time.

      November 1, 2013 at 10:56 am |
    • Long time baker

      Burnt graham cracker crust? That's new. Burnt dough crust I've heard plenty and the foil trick works great. Sounds like your stove isn't heating evenly. Might want to have that checked out.

      November 4, 2013 at 6:42 am |
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