For the pastry: Sift together the flour, baking powder and sugar in a mixing bowl. Combine the butter, egg yolks, whole egg and lemon zest in a separate bowl. Mix the wet ingredients into the dry ingredients, and then knead into a dough. Let rest 30 minutes.
Preheat the oven to 350 degrees F.
For the filling: Whip the egg whites with 1/2 of the sugar to stiff peaks in a mixing bowl. Whip the remaining sugar, ricotta and lemon zest together in a separate bowl, and then gently fold into the egg whites.
Roll out the pastry and fit into a pie plate. Spread the ricotta filling into the crust, sealing with more pastry as you would a pie. Bake 15 to 20 minutes.