Flatten the bread slices slightly with a rolling pin, and with a four-and-a-half inch cookie cutter, cut into four rounds.
Cut each round in half, then press the two halves into each muffin cup, overlapping slightly and making sure bread comes up to the edges. Use extra bread and crusts to patch any holes if necessary.
Brush with remaining butter.
In a large skillet, cook the bacon until almost crisp, about four minutes, flipping once.
Lay one bacon slice in each bread cup and crack an egg over each. Season with salt & pepper.
Bake until egg whites are just set, about twenty-five minutes. The bacon will continue to cook in the oven.
Run a small knife around cups to loosen toast cups.