Chef Ina Garten has a recipe for homemade croutons in her cookbook “Cook Like a Pro” which are so irresistible that Garten features the recipe on the cookbook's cover.
Start with a preheated pan, add a couple of tablespoons of olive oil, then the bread. The cubes won't toast evenly if you add cold oil and bread to the pan simultaneously.
Garten redistributes the croutons with a skillet flip to ensure the bread is evenly seasoned with kosher salt and freshly ground black pepper, and is golden brown on all sides.
Ina Garten uses olive oil in her recipe, but any fat will work. A combination of butter and oil is delicious, or for a smoky element, pan-fry the bread in bacon grease.