1. Preheat oven to 425°. Unroll piecrusts; stack on a lightly greased surface. Roll stacked piecrusts into a 12-inch circle. Fit piecrust into a 10-inch deep-dish tart pan with removable bottom; press into fluted edges. Trim off excess piecrust along edges. Line piecrust with aluminum foil or parchment paper, and fill with pie weights or dried beans. Place pan on a foil-lined baking sheet. Bake 12 minutes. Remove weights and foil, and bake 8 more minutes. Cool completely on baking sheet on a wire rack (about 15 minutes). Reduce oven temperature to 350°.
2. Meanwhile, cook onions in hot oil in a large skillet over medium-high heat, stirring often, 15 to 20 minutes or until onions are caramel colored. Remove from heat, and stir in parsley and bacon. Place half of onion mixture in tart shell, and top with half of cheese; repeat with remaining onion mixture and cheese.
3. Whisk together half-and-half and next 4 ingredients; pour over cheese.
4. Bake at 350° for 40 to 45 minutes or until set. Cool on baking sheet on a wire rack 15 minutes before serving.