In a medium bowl, mix the flour, butter, and powdered sugar until well combined. Press into an ungreased 8x8x2-inch or 9x9x2-inch baking pan, building up the edges about half an inch.
Bake the crust for 20 minutes.
Beat the filling ingredients with an electric mixer on HIGH speed for about 3 minutes or until the mixture is light and fluffy. Pour the mixture over the hot crust.
Bake for 25-30 minutes or until no indentation remains when the center is lightly touched. Cool in the pan on a wire rack.
Just before serving, dust with powdered sugar, if desired. Cut into 1-1/2 to 2-inch bars.
Notes
Line the baking pan with parchment paper that hangs slightly over the edges to make it easier to get the bars out!
These bars can be left at room temperature for up to 3 days or refrigerated for up to 7 days!