Melt the butter in a large skillet over moderate heat and cook until it foams. Add the bread cubes and toss to coat with the butter. Transfer the bread to a baking sheet. Immediately sprinkle with the cheese and toss again while warm to melt the cheese.
Bake, stirring once or twice, until the croutons are crisp and lightly colored on the outside but still soft within, about 15 minutes. Let cool. Store in an airtight container.