Arrange a rack in the lower third of the oven.

Dust your countertop lightly with flour. Use a rolling pin to roll the dough into a 12-inch circle, about ⅛ to ¼-inch thick. (If using store-bought pie dough, unroll or unfold it.) Transfer the dough to a 9-inch deep-dish pie plate, gently pressing it into the bottom. Roll and fold the overhang of dough under itself to build up the crust edge, trimming any excess as you work around the pie dish. Use your fingers or a fork to crimp the edges of the pie dough. Transfer the crust to the fridge to chill while the oven preheats.

In a large bowl using a hand mixer, beat the egg whites on medium-high speed until foamy, about 1 minute. With the mixer running, add ¼ cup (50g) of the sugar in a slow stream. Continue beating until stiff peaks form, about 4 minutes. When you lift the beaters out of the bowl, the whipped egg whites should stand up and hold a point.

In another large bowl, use your fingertips to rub the lemon zest into the remaining 1 cup (200g) granulated sugar, infusing the sugar with the flavorful oils from the zest. Pour in the melted butter, and add the egg yolks. Whisk together until smooth and pale yellow, about 1 minute. Add the flour and salt, and whisk until combined. Pour in the lemon juice, and whisk to incorporate. Pour in the milk, a splash at a time. Once you've incorporated about half of the liquid, you can pour in the rest and whisk to combine. The batter will be thin, like crêpe batter.

Add the beaten egg whites, then whisk gently until there are no large lumps. Don’t overmix—there should still be a layer of foam on top of the batter.

Pour the filling into the prepared crust. Bake for 15 minutes, then lower the temperature to 300°F without opening the oven door. Continue baking until the filling is golden brown and set with a very slight jiggle in the center, 35 to 45 minutes longer.

Transfer the pie to a wire rack and let cool completely. Cover lightly with aluminum foil and chill in the refrigerator for at least 4 hours (ideally overnight) before slicing and serving. Store leftover pie, covered, in the refrigerator for up to 4 days. Love the recipe? Leave us stars and a comment below!