2 cups all-purpose flour, plus more for work surface
1/4 cup sugar
1/2 teaspoon baking powder
1/4 teaspoon salt
1/2 cup (1 stick) unsalted butter, cut into 8 pieces
2 large eggs, lightly beaten
1 pound whole milk ricotta
3 large eggs
1/4 cup freshly grated Parmesan cheese
1/4 pound mozzarella cheese
1/4 pound prosciutto, thinly sliced
2 tablespoons chopped fresh parsley
1/2 teaspoon freshly ground pepper
1 large egg, lightly beaten, for brushing
Preheat oven to 375 degrees with rack in center. Prepare crust: In the bowl of a food processor, combine flour, sugar, baking powder, and salt. Pulse to combine. Add butter; pulse until mixture resembles cornmeal. With processor running, add eggs and process until dough comes together and forms a ball, about 1 minute. Transfer to a lightly floured work surface, and knead until smooth, 3 to 5 minutes.
Prepare filling: In a large bowl, stir together ricotta, eggs, Parmesan, mozzarella, prosciutto, parsley, and pepper; set aside.
Divide dough into 2 pieces, one slightly larger than the other. Roll larger piece into a 12-inch circle; gently transfer to a 9-inch glass pie dish. Place filling in pie plate and spread evenly; set aside.
Roll remaining dough into a 9-by-9-inch square; cut into 1/2-inch wide strips. Using strips, form a lattice pattern over filling. Trim bottom crust, leaving a 1/2-inch overhang. Crimp edges to seal. Brush with egg, and bake until filling is firm, 40 to 45 minutes. Let cool completely before serving.