Prepare Deep-Dish Pastry Shell; set aside on baking sheet. Preheat oven to 325 degrees F.
Core and cut 2 of the pears into 1/2- to 3/4-inch cubes. Thinly slice the remaining pear and reserve.
Melt 1 tablespoon of the butter in a large skillet over medium-high heat. Add the cubed pears and sugar; cook, stirring occasionally, for 7 to 8 minutes or until lightly browned. Transfer to the pre-baked pastry shell and top with blue cheese; set aside. Melt the remaining 1 tablespoon butter in the skillet and add the pear slices. Cook, stirring occasionally, for 3 to 4 minutes or until just softened; set aside.
For the custard, in a blender combine the eggs, yogurt, milk, salt, pepper, and nutmeg. Blend until frothy.
Place the springform pan with the pastry shell on a baking sheet. Gently pour in the custard. Arrange the reserved pear slices in a spoke pattern on top of the quiche. Bake 1 hour 20 minutes to 1 hour 30 minutes until the top is lightly browned and the custard is just set (165 degrees F) but still jiggles slightly in the center. Let stand 30 to 40 minutes. With a serrated knife, cut the pastry shell flush with the top of the pan. Carefully remove the springform pan ring. Top with additional blue cheese and, if desired, sage leaves. Cut into wedges.
Deep Dish Pastry Shell
In the bowl of a food processor combine the flour and salt. Add the butter and pulse until the mixture resembles coarse crumbs. Combine the egg and water in a small bowl; add to the food processor and pulse until the mixture just begins to clump together. Transfer the mixture out onto a sheet of plastic wrap; fold the wrap over and press the crumbs until they hold together; shape into a circle. Wrap and chill at least 30 minutes.
Turn the dough out onto a lightly floured surface and roll it out to a 15-inch circle. Carefully roll the pastry around the rolling pin and transfer to a 9x2 1/2-inch springform pan, pressing it into the sides. Trim the overhanging pastry to 1 inch and press it firmly against the outside of the ring to help prevent it from shrinking. Use the trimmings to fill any cracks. Freeze the shell for 20 minutes.
Preheat the oven to 400 degrees F. Place the springform pan on a baking sheet. Line the pastry shell with a double thickness of aluminum foil long enough to overhang the sides. Bake about 20 minutes or until the edge of the dough is lightly browned. Remove the foil and continue baking the pastry shell for 10 to 15 minutes longer, or until lightly browned on the bottom. Transfer the baking sheet to a rack and let the pastry cool.