Cook 6 ounces diced slab bacon in a skillet; drain. Cook 2 sliced leeks in 3 tablespoons drippings. Spread the leeks, 2/3 cup shredded Gruyère and the bacon in a prebaked 9-inch tart crust or pie crust. Whisk 2 whole eggs, 2 yolks, 1 cup cream, and salt and pepper; pour over the cheese. Bake at 375 degrees F, 25 minutes