Preheat the oven to 350F.

In the bowl of the food processor, add the flour, powdered sugar and butter. Run the machine until coarse crumbs form and the mixture sticks together when pinched.

Line a 9x9 pan with parchment paper. Press the crust firmly and evenly into the pan. Bake for 15 minutes, until golden brown.

While the crust is baking, make your filling. Whisk together the zest, juice, eggs, sugar, flour and baking powder. When the crust is finished baking, whisk the filling again and pour over the crust. Return to the oven for 25-30 minutes, until the filling is set and the top is golden brown.

Remove from the oven and let cool on a wire rack. Sprinkle with powdered sugar.