Make the dough:
Combine the flour, sugar, salt, and baking powder in a zip-top bag; shake to mix and chill in the freezer for about 30 minutes. Add half of the butter and shortening to the bag and toss to coat with flour. Transfer the mixture to a food processor. Give it four 1-second pulses and then process for 3 to 4 seconds. Add the remaining butter and shortening and pulse again 4 times; then process until the mixture has the texture of coarse meal with some pea-size pieces of butter and shortening, 3 to 4 seconds.
Empty the mixture into a large bowl. Drizzle 1 Tbs. of the ice water around the side of the bowl and use a fork to push the flour mixture from the edges towards the center; repeat with a second tablespoon of ice water. Clusters of dough will form and become larger with each addition of water. After adding 2 Tbs. water, test the dough by pressing a small handful of clusters clusters together and then breaking them apart. If they feel dry and crumble easily, add more water, 1 Tbs. at a time (up to 4 Tbs. total), until the clusters feel moist and bind together.
Gather and press the dough into a ball, flatten it into a 4- to 5-inch disk, and dust with flour. Wrap with plastic and refrigerate until cold but still pliable enough to leave a slight imprint when pressed with a fingertip, about 1 hour.
Shape the crust:
Butter the bottom, sides, and rim of a 9-inch glass pie plate.
On a floured pastry cloth or lightly floured work surface, roll the dough with a floured rolling pin (preferably covered with a rolling pin sleeve) into a 13-inch circle that’s about 1/8 inch thick. Roll the dough around the rolling pin, unroll it over the pie plate, and gently fit it into the plate without stretching. Trim the dough with scissors to a 3/4- to 1-inch overhang. (Reserve the dough scraps, without pressing them into a ball, in case you need to patch the shell later.) Roll the overhang under itself and flatten it slightly to cover the rim of the pie plate completely. Chill for at least 30 minutes before baking.
Bake the crust:
Position a rack in the lower third of the oven and heat the oven to 425°F. Using a fork, lightly prick the bottom and sides of the crust at 1-inch intervals (without going all the way through the crust). Fit a buttered 12-inch piece of aluminum foil over the crust, buttered side down. Fill 1/2 to 3/4 inch deep with dried beans or pie weights—do not overfill.
Bake the crust on a rimmed baking sheet until the edges begin to brown, 15 to 18 minutes. Let stand on a cooling rack for about 30 seconds, and then carefully remove the foil and beans. If the foil doesn’t release easily, don’t force it—bake for a few minutes more and try again. If any holes or tears appear, patch them by placing small pieces of the reserved dough scraps over the holes, let stand for a few seconds, and then gently tap them with your finger until they adhere. Reduce the oven temperature to 375°F and continue to bake the crust until deep golden-brown all over, 16 to 20 minutes more. Cool on a rack for at least 15 minutes. (Keep the oven on.)
Make the filling:
In a heavy-duty 3-quart nonreactive saucepan, whisk together (preferably with a tapered sauce whisk) the sugar, cornstarch, and salt. Whisk in 1/4 cup cold water until the mixture is smooth. Then whisk in another 1-1/4 cups cold water until combined. Cook over medium to medium-low heat, stirring occasionally at first with a heatproof spatula, then continuously as the mixture comes to a boil (you will see a few large bubbles pop), turns glossy, and thickens into a semi-translucent gel, 4 to 6 minutes. Whisk briefly to smooth out the mixture; then reduce the heat to low and cook 1 minute more, gently pulling the mixture from the sides to the center with the spatula to prevent scorching. Remove the pot from the heat.
In a medium bowl, lightly whisk the egg yolks. Gently whisk about 1/2 cup of the gel into the egg yolks; repeat with another 1/2 cup gel. Pour the yolk mixture into the pot and gently whisk to combine. Over low to medium-low heat, cook the filling, gently pulling it from the sides to the center with the spatula, until it begins to boil (you will see a few large bubbles pop), 4 to 6 minutes. Continue to cook, stirring as before, until the mixture thickens further(don’t worry if it clumps at this point), about 1 minute more. Remove the pot from the heat and dot the filling with the butter, pushing it under the surface; let stand for a minute to melt. Gently whisk in the lemon juice and zest until smooth.
Sprinkle the ground gingersnaps over the bottom of the pie crust; pour the filling over the crumbs and smooth the top with the spatula. Let cool to room temperature before making the meringue, at least 30 minutes.
Make the meringue:
Bring 1/2 inch of water to a simmer in a pot that will hold the bowl of a stand mixer without letting it touch the water. Reduce the heat to low. Put the egg whites in the bowl off the heat and whisk (preferably with a balloon whisk) until frothy. Add the sugar about 2 Tbs. at a time, whisking for about 5 seconds between additions.
Put the bowl over the pot and whisk gently but constantly (you are not trying to incorporate air, but to keep the whites moving so they don’t cook) until the whites are very warm to the touch (they will register 115°F to 120°F on an instant-read thermometer) and the sugar is thoroughly dissolved (lift a ribbon of whites from the bowl with the whisk and rub the whites between your fingertips—you should feel no grit), 2 to 4 minutes.
Add the vanilla and cream of tartar, transfer the bowl to the stand mixer, fit with the whisk attachment, and beat, gradually increasing the speed from low to medium high over the course of 1 minute, until the egg whites form thick, glossy medium-firm peaks (they should hold their shape but curl at their tips), 3 to 5 minutes total.
Using a soup spoon, drop some of the meringue in mounds in a ring around the edge of the filling. With the back of the spoon, gently spread the dollops of meringue over the entire surface of the filling and all the way to the crust’s edge. It is essential that all of the filling be completely covered by the meringue, without any air pockets, and that the edge of the meringue be anchored to the rim of the crust. Mound the remaining meringue on top and press with the back of the spoon to eliminate any air pockets without deflating the meringue. Make decorative peaks with the back of the spoon.
Bake the pie until the meringue peaks brown, 5 to 7 minutes. Cool the pie on a rack away from drafts to prevent the meringue from shrinking. Let stand at least 1 hour before serving.
To slice, rinse a sharp, thin-bladed knife in hot water and shake off the excess before making each cut.
Make Ahead Tips
Lemon meringue pie is best eaten the day it’s made, but leftovers will keep, loosely tented with aluminum foil and refrigerated, for up to 3 days. Never cover with plastic wrap—too much condensation will form under the wrapping. Do not freeze.
The disk of pie dough will keep for up to 3 days in the refrigerator or 3 months in the freezer. Thaw frozen dough in the refrigerator for at least 12 hours; then let stand at room temperature until pliable.
nutrition information (per serving):
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Photo: Scott Phillips