Lemon-Butter Snowbars

Preheat oven to 350°F (175°C). In a medium bowl, combine 1 1/3 cups flour, 1/4 cup sugar, and 1/2 cup softened butter. Beat at low speed, scraping the bowl often, until the mixture is crumbly, about 2 to 3 minutes. Press onto the bottom of an 8-inch square baking pan. Bake for 15 to 20 minutes, or until the edges are lightly browned. Meanwhile, in a mixer bowl, combine 3/4 cup sugar, 1 cup softened butter, egg yolks, lemon or vanilla extract, 2 cups flour, and salt. Beat at low speed with an electric mixer until smooth. Pour over the crust, then continue baking for 18 to 20 minutes, or until the filling is set. Sprinkle with powdered sugar. Cool before cutting into bars.