Over medium heat, cook bacon in a frying pan. Fry until the bottom of the bacon starts to brown. Flip the bacon and continue cooking until the bacon is crisp but still bendy. Remove the bacon from the pan and place on a plate on top of a sheet of paper towel.

Butter one side of each bread slice.

Add two pieces of bacon to each slice of bread, on top of the butter. Add ketchup if you want. 

Put the slices of bread together so the bacon is together.

Slice in half and enjoy.