Begin by toasting the bread slices until golden and crisp, then set aside.
Place bacon strips in a cold skillet and cook over medium heat, flipping occasionally, until they turn crispy and smell fragrant, about 8–10 minutes. Drain on paper towels.
Remove the bacon and set aside. Carefully discard excess bacon fat while leaving about a teaspoon in the pan.
Add butter to the skillet and let it melt over medium heat. Crack in the egg, being gentle to keep the yolk intact.
Cook the egg for about 2–3 minutes until the whites are set but the yolk remains runny. Season with salt and pepper to taste.
Using a spatula, carefully lift the fried egg and place it onto one slice of toasted bread.
Layer the crispy bacon slices on top of the egg for added crunch and smoky flavor.
Cover with the second slice of toast, pressing down lightly to make a compact, handheld sandwich.
Slice the sandwich in half if desired, and enjoy while warm, with the yolk still runny and the bacon crispy.