Preheat oven to 450 degrees F (230 degrees C). Bake pre-made pastry shell in oven for 8 minutes or until crust is set and dry. Remove from oven and turn down temperature to 325 degrees F (165 degrees C).

In a large skillet, cook ham. Drain and reserve 2 tablespoons of drippings. Cook onion in skillet with reserved drippings; cook until onion is tender and then drain.

In a large bowl, mix together milk, salt and eggs. Stir in ham and onion. In a separate bowl, toss cheese and flour together, then add to egg mixture. Be sure to mix well. Pour egg mixture into pie crust.

Bake in preheated oven for 35 to 40 minutes, or until knife inserted in center of quiche comes out clean. If necessary, cover edge of crust with foil while baking to prevent burning or overbrowning.

Let stand for 15 minutes before serving.