Combine the flour and sugar in a mixing bowl. Cut in the butter or margarine with a pastry blender until the mixture is crumbly.
Press the dough into a 9-inch square cake pan. Bake at 350°F for 10 minutes. Let the crust cool for 10 minutes before adding the filling.
To make the filling, beat the eggs and brown sugar together in a small bowl with an electric mixer until they are light and fluffy. Stir in the remaining ingredients and pour the mixture over the cooled crust.
Bake at 350°F for 20-25 minutes, or just until set and golden.
Cool and cut into squares for serving.
Makes about 12 butter tart squares or more if they are cut smaller.