Pre-heat oven to 375 degrees.
Using a cookie cutter, egg fry ring or empty can, cut six rounds of bread. Using a rolling pin or your hands, flatten rounds slightly.

Cut rounds in half and butter one side. Place buttered-side out in the muffin cups, using extra bread to fill in any gaps (if needed). (If using a pan with more than 6 cups, space your egg cups so everything cooks evenly).

Fry bacon in a skillet until partially cooked, 4-5 minutes. (It will finish cooking in the oven)

Place the bacon in the cup, covering the bottom. (It may be easier to first cut each piece in half).

Crack an egg in each cup. Season with salt and pepper. Bake until egg whites are just set, about 20 minutes.