The butt end of bread will sit around forever and go bad, but croutons, designed to sit around forever, will be gone in mere moments. Yes, I'm on a crouton kick.
Preheat the oven to 350 degrees F.
Cube the bread into 1/2 inch cubes and spread onto cookie sheets. The cubes of bread may touch but should not pile up on the pan. Artisan (i.e., homemade) bread is best, but even processed bread will work.
Melt butter. Do not use margarine. You can use olive oil instead of the butter. A mix of about 1/2 butter, 1/2 olive oil is nice (just mix in the olive oil after melting the butter). I use about 1/4 c. butter or olive oil per 2c. bread, but then, I believe a diet is about eating less rather than eating diet food. Pour butter/oil over bread and stir until it's soaked up.
Sprinkle the bread with salt and ground pepper. Stir.
If you like, about 1/4c. shredded hard cheese (parmesan or even sharp cheddar) can be added. Stir. Reduce the amount of butter by about 1/3 if you're using an oily cheese. (Or not, if you don't mind the croutons being more chewy than crunchy.)
Put in the oven. Take out every few minutes to stir around. The croutons are done when a) they're crunchy and b) smell toasty. Cheese should be browned but not burnt.
More butter/oil/cheese = chewier croutons. Less = crunchier, drier croutons.
Last time, I made rye croutons with 1/2 butter, 1/2 Tunesian olive oil (thanks, Margie!), salt and pepper. Yummy. Oh, and it makes an excellent opportunity to roast garlic cloves, too, which will scent the croutons without making them overpoweringly garlicky.