Preheat the oven to 180°C.
Apply the butter on all the bread slices. Cut them into small cubes. I made 16 cubes out of one slice.
Grease a shallow baking pan, preferably dark colored one. Arrange the cubes on it apart from each other.
Bake for 7-10 minutes. Turn the croutons and bake the other side for another 7 minutes. The second side will get browned faster.
Serve with soups or salads. Left overs can be cooled and stored in air tight containers.