Stir the flour and baking powder together in a bowl; set aside. In a second large bowl cream the butter and 1/2 cup sugar until light and fluffy. Whisk in 3 eggs one at a time and stir in the vanilla. Gradually mix in the flour mixture to make a soft dough. Divide the dough in half and shape into two balls. Working on a lightly floured surface roll out each ball to fit two 25cm pie dishes. Line the pie dishes with the base and refrigerate until needed.
Bring the water to a boil in a saucepan and stir in the rice. Reduce the heat to medium-low, cover and cook for 20 minutes. Stir in the milk. Continue cooking, stirring frequently until the mixture thickens. Set aside to cool.
Preheat oven to 165 degrees C.
Meanwhile whisk the ricotta cheese, 1 1/2 cups sugar, lemon juice, lemon peel and 6 eggs together in a mixing bowl until smooth and frothy. Stir in the cooled rice mixture until evenly blended. Pour into the pie bases.
Bake pies in preheated oven until the filling is set and tops are golden brown: about 90 minutes. Cool on cake racks.