01 -
Preheat oven to 350°F while preparing pie components.
02 -
Sauté sliced onion in reserved bacon drippings over medium heat until deeply caramelized, about 10 minutes; transfer onions to a plate to cool.
03 -
Arrange half of the cooked onions evenly in the pie shell, top with half the sliced tomatoes and half the chopped bacon. Repeat with the remaining onions, tomatoes, and bacon to build layers.
04 -
In a medium bowl, combine mozzarella cheese, mayonnaise, sour cream, flour, garlic powder, salt, and black pepper until uniformly mixed.
05 -
Spread the cheese mixture evenly over the layered ingredients in the pie shell.
06 -
Place the pie on a baking sheet and bake at 350°F for 35 to 40 minutes, until the top is bubbling and golden brown.
07 -
Allow pie to cool for several minutes before slicing. If desired, garnish with chopped parsley or chives before serving.