Step 1

Place 1 1/2 sticks unsalted butter and 4 large eggs on the counter. Let both sit at room temperature until the butter is softened.

Step 2

Arrange a rack in the middle of the oven and heat the oven to 350ºF. Line the bottom and all 4 sides of a 9x9-inch square baking pan with 2 sheets of parchment paper, positioning them perpendicular to each and hanging over all four sides by at least 1 inch to form a sling.

Step 3

Finely grate the zest of 1 large lemon into the bowl of a stand mixer (or large bowl if using an electric hand mixer). Add 1/4 cup granulated sugar and use your fingers to rub the zest into the sugar until fragrant.

Step 4

Add the butter and 1/2 teaspoon kosher salt to the bowl of butter. Beat with the paddle attachment on medium speed until creamy, about 2 minutes. Scrape down the sides of the bowl with a flexible spatula.

Step 5

Add 1 3/4 cups all-purpose flour. Beat on medium speed until fine crumbs of dough form, 30 seconds to 1 minute. Transfer to the baking pan and use your hands to press into an even layer.

Step 6

Bake until the crust is light golden-brown around the edges, 15 to 22 minutes. Meanwhile, make the filling.

Step 7

Crack the eggs into a medium bowl and whisk until beaten. Finely grate the zest of 1 large lemon (about 1 tablespoon) into the bowl.

Step 8

Juice the zested lemon plus 4 more as needed until you have 3/4 cup. Add the juice, 1 1/2 cups granulated sugar, and 1/2 teaspoon kosher salt to the bowl of eggs. Whisk until smooth. Sift 1/3 cup all-purpose flour over the mixture and whisk until smooth and combined.

Step 9

When the crust is ready, immediately pour in the filling while the crust is hot. Bake until the filling is just set with a slight wiggle in the center, 18 to 20 minutes. Place the pan on a wire rack and let cool for about 1 hour. Refrigerate for at least 3 hours or up to overnight.

Step 10

Grasping the excess parchment, lift the slab out of the baking dish and place on a cutting board. Cut into 16 pieces, dipping the knife in hot water and wiping it dry between each cut for the cleanest-looking pieces. Right before serving, place some powdered sugar in a fine-mesh strainer and generously dust over the lemon bars in an even layer.