Mix flour, butter and powdered sugar. Press into the bottom of an ungreased 9x13 inch (25x38 cm) rectangular pan, building up the edges a bit. Bake crust 15-20 minutes, until golden. Remove from oven.
While the crust is baking, beat filling ingredients with electric mixer on high speed for about 2-3 minutes until the sugar is dissolved and the mixture is light and fluffy. Pour filling over hot crust. The filling will be liquid before baking. Carefully transfer to oven and bake for an additional 20-25 minutes until lightly browned and the center is set.
Cool in the pan on a wire rack. Dust with powdered sugar and cut into bars. Store in a tightly sealed container in the refrigerator for up to 3 days. Allow bars to come to room temperature before serving.
Notes
The crust mixture is quite crumbly before pressing it into the pan. Just press it down and it’ll make a fine crust. If it sticks to your fingers, try using the back of a soup spoon or lay a piece of parchment paper over the crust while pressing it in. Also don’t forget to build up the edges of the crust about ½ inch (1 cm).