A friend of mine makes the best lemon squares. Even though you have the filling, I'm going to share the entire recipe for anyone that's interested. Have you considered using a simple phyllo dough? Anyhow, here goes:
2 cups flour
1/2 cup sifted confectionery sugar
1 cup butter or margarine
4 beaten eggs
2 cups granulated sugar
1/2 cup of fresh lemon juice (about 1 lemon)
1/4 cup flour
1/4 tsp. baking powder
Sift together the 2 cups flour with the confectioners sugar. Cut butter or margarine in until mixture comes together and is crumbly. Press into a pan (9 x 12?) sprayed with Pam. Bake at 350 oven for 20-25 minutes until light brown.
Beat together eggs, granulated sugar and lemon juice. Sift together 1/4 cup flour and baking powder. Stir into the egg mixture. Pour over the baked crust.
Bake 350 for 25 minutes. Sprinkle with confectioners sugar. Cool. Cut into bars.