Preheat oven to 425 degrees. Unroll pie crusts and stack on a lightly greased surface. Roll into at least a 12-inch circle, depending upon the size of your pan. Mold pie crust into a deep dish pie pan or 10-inch deep dish tart pan with removable bottom. Trim off excess pie crust along edges. Place a sheet of aluminum foil or parchment paper on pie crust and place pie weights or dried beans on top. Place on a foil-lined baking sheet and bake for 10 minutes. Remove weights and foil and bake an additional 8 minutes. Cool completely, about 15 minutes.
Reduce oven temperature to 350 degrees.
While piecrust is baking, cook onions in olive oil, butter, and bacon grease in a large skillet over medium-low heat. Stir often and cook for 15 to 20 minutes, until caramel colored. Remove from heat and add bacon crumbles to pan with onions.
Place half of onion-bacon mixture in piecrust and top with half of cheese. Repeat with remaining onions and cheese.
In a medium bowl, whisk together half-and-half, eggs, salt, pepper, and nutmeg. Pour over cheese.
Bake for 40 to 45 minutes at 350 degrees, or until set. Cool 15 minutes before serving.