Combine flour, sugar and salt. Mix well. Grate butter on large holes of box grater. Add to flour mixture; combine well until mixture resembles coarse meal. Press into 13 x 9-inch baking dish. Bake 20 minutes.
Combine filling ingredients. Whisk well. Pour over warm crust and bake 20 minutes or until filling is set. Let cool. Sprinkle with powdered sugar.