Lemon Squares

(From America's Test Kitchen)

The Crust:
1 3/4 cups unbleached all-purpose flour
2/3 cup confectioners' sugar , plus extra to decorate finished bars
1/4 cup cornstarch
3/4 t table salt
12 T unsalted butter (1 1/2 sticks), at very cool room temperature, cut into 1-inch pieces, plus extra for greasing pan

Lemon Filling:
4 large eggs , beaten lightly
1 1/3 cups granulated sugar
3 T unbleached all-purpose flour
2 t grated lemon zest from 2 large lemons
2/3 cup lemon juice from 3 to 4 large lemons, strained
1/3 cup whole milk
1/8 t table salt

1. For the crust: Adjust oven rack to middle position and heat oven to 350 degrees. Lightly butter a 13-by-9-inch baking dish and line with one sheet parchment or wax paper. Dot paper with butter, then lay second sheet crosswise over it.

2. Pulse flour, confectioners’ sugar, cornstarch, and salt in food processor fitted with steel blade.

3. Add butter and process to blend, 8 to 10 seconds, then pulse until mixture is pale yellow and resembles coarse meal, about three 1-second bursts.

4. Sprinkle mixture into lined pan and, following illustration 2, press firmly with fingers into even, 1/4-inch layer over entire pan bottom and about 1/2-inch up sides. Refrigerate for 30 minutes, then bake until golden brown, about 20 minutes.

5. For the filling: Meanwhile, whisk eggs, sugar, and flour in medium bowl, then stir in lemon zest, juice, milk, and salt to blend well.

6. To finish the bars: Reduce oven temperature to 325 degrees. Stir filling mixture to reblend; pour into warm crust. Bake until filling feels firm when touched lightly, about 20 minutes.

7. Transfer pan to wire rack; cool to near room temperature, at least 30 minutes.

Sprinkle confectioners’ sugar over bars, if desired.