Preheat the oven to 375°F.

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. 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.

In another large bowl, use your fingertips to rub the lemon zest into the remaining 1 cup (200g) granulated sugar. 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, whisking to combine.

Add the beaten egg whites, then whisk gently until there are no large lumps. Don’t overmix.

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.