Quiches are a perfect way of repurposing leftovers from dinner into a delicious breakfast. The leftover caramelized onions and thyme from a chicken entrée the night before blend nicely with the leftover cheese from homemade macaroni and cheese. Feel free to substitute the cheeses for whatever you have in the refrigerator. In fact, this whole recipe is nothing but a framework for repurposing leftovers. Endless creative quiche-friendly ingredient combinations await you in your refrigerator.