Preheat oven to 375 degrees F. In a 10-inch oven-going skillet with flared sides melt butter over medium heat. Stir in quince or apple slices, sugar, and sage. Cook over medium heat until bubbly, stirring occasionally. Reduce heat to medium-low. Cook, uncovered, about 20 minutes more or until quince or apples are very tender (if using quince, mixture will thicken and turn a deep golden brown), stirring occasionally. Remove from heat.
On a lightly floured surface, use your hands to slightly flatten Savory Prosciutto Pastry dough. Roll dough from center to edge into a 10-inch circle. Cut slits in the center of the pastry. Carefully wrap pastry circle around rolling pin. Unroll pastry over the quince or apple mixture in the skillet, being careful not to stretch the pastry.
Bake in the preheated oven about 30 minutes or until pastry is golden and filling is bubbly. Cool in skillet on a wire rack for 5 minutes. Invert onto a large serving plate. Lift off skillet. Replace any fruit slices left in skillet. If desired, sprinkle with cheese and sage. Cool for 20 minutes more. Serve warm.
Savory Prosciutto Pastry
In a medium bowl stir together flour, sugar, and a pinch ground black pepper. Using a pastry blender, cut in butter until pieces are pea size. Stir in finely chopped prosciutto. In a small bowl use a fork to lightly beat egg; stir egg and 1 tablespoon cold water into prosciutto mixture. Stir until all of the prosciutto mixture is moistened, adding another 1 tablespoon cold water if necessary. Gather mixture into a ball, kneading gently until it holds together.