Difficulty: Easy - for beginners
1 3/4 c (8.75oz) all-purpose flour
2/3 c (2 2/3 oz) confectioners' sugar, plus extra for garnish
1/4 c cornstarch
3/4 tsp salt
12 T unsalted butter, chilled and cut into 1-inch pieces
4 large eggs, lightly beaten
1 1/3 cups (9 1/3 oz) granulated sugar
3 T all-purpose flour
2 tsp grated lemon zest plus 2/3 cup juice (4 lemons)
1/3 c whole milk
1/8 tsp salt
1. FOR THE CRUST: Put oven rack in middle of oven and heat to 350F. Make foil sling by folding 2 long sheets of aluminum foil so that they are as wide as 13 x 9-inch baking pan. Lay sheets of foil in pan perpendicular to one another, with extra foil hanging over edges of pan. Push foil into corners and up sides of pan, smoothing foil flush to pan. Grease foil and set aside.
2. Process flour, confectioners' sugar, cornstarch, and salt in food processor until combined, 15 seconds. Add butter and process to blend, 8-10 seconds, then pulse until mixture is pale yellow and resembles coarse meal, about 3 pulses. Sprinkle mixture into prepared pan and 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.
3. FOR THE FILLING: Whisk eggs, sugar, and flour in medium bowl, then stir in lemon zest and juice, milk, and salt to blend well.
4. Reduce oven temp to 325F. Stir filling mixture to reblend; pour into warm crust. Bake until filling feels firm when touched lightly, about 20 minutes. Transfer pan to wire rack; let cool to near room temperature, at least 30 minutes. Cut into squares and sieve confectioners' sugar over squares, if desired. (Bars can be refrigerated for up to 2 days; crust will soften slightly.)