Lemon Squares

From Beat This! by Ann Hodgman
Crust
1 cup all-purpose flour
8 tbsp unsalted butter, cut into 1/2 slices
2 tbsp sugar
2 tsp grated lemon or lime zest
pinch salt

Filling
1 1/2 cups sugar stirred together with 3 tbsp all-purpose flour
1 1/2 tbsp grated lemon or lime zest
3/4 cup fresh lemon or lime juice
3 large eggs
3/4 tsp baking powder

Preheat the oven to 375. Butter an 8 inch square baking pan.

Crust: Place all ingredients in a food processor. Process until mixture begins to form a ball. Pat the mixture into the bottom of the prepared pan and bake for 15-20 minutes or until a pale golden all over. Take the crust out of the oven and turn down to 350.

Filling: Clean the food processor and place all the filling ingredients inside. Process until very smooth. Pour into partially baked crust and bake for 20-25 minutes or until the filling is set and beginning to brown around the edges.
Allow to cool, then chill well in the fridge.