Line a sheet pan with parchment paper and place a baking rack on the sheet pan. Arrange the bacon in one layer on the baking rack. Bake for 25 minutes until it's deep golden and crispy. Transfer the bacon to a plate lined with paper towels.
Toast the bread slices and slather them with butter.
Arrange 4 slices of bacon on every other slice of bread and top with second slice of bread to make four sandwiches. Slice each sandwich in half diagonally and serve.