Preheat oven to 375. Lightly butter 6 standard muffin cups.
With a rolling pin, flatten bread slices slightly and, with a 4 1/2 -inch cookie cutter, cut into 8 rounds. Cut each round in half, then press 2 halves into each muffin cup, overlapping slightly and making sure bread comes up to edge of cup. Use extra bread to patch and gaps.
Brush bread with remaining butter.
In a large skillet, cook bacon over medium, until almost crisp, 4 minutes, flipping once.
Lay 1 bacon slice in each bread cup and crack an egg over each.
Season with salt and pepper. Bake until egg whites are just set, 20 to 25 minutes.
Run a small knife around cups to loosen toasts, serve immediately.