Step 1

Place 2 sticks unsalted butter in the bowl of a stand mixer (or large bowl if using an electric hand mixer). Let sit at room temperature until softened. Coat an 8- or 9-inch square metal baking pan with more butter.

Step 2

Beat the butter on high speed with the paddle attachment until fluffy, 3 to 5 minutes. With the mixer running, gradually add 3/4 cup powdered sugar and continue to beat until pale and fluffy.

Step 3

Stop the mixer. Sift 2 cups all-purpose flour into the bowl, then add 1/4 teaspoon coarse salt. Mix on low speed until just combined. Transfer to the prepared pan and pat to an even thickness no more than 1/2-inch thick. Refrigerate for at least 30 minutes. Meanwhile, arrange a rack in the middle of the oven and heat the oven to 300°F.

Step 4

Slice the dough into rectangles or squares in the pan. Bake until golden-brown and the middle is firm, 45 to 60 minutes. Let cool completely. Re-slice, if needed, before serving.