Diced bread tossed in garlic butter and baked until dry and crisp. Three ingredients, twenty minutes, and both the butter and the garlic are optional if you only want plain toasted cubes.
Day-old bread is what this wants. Fresh bread holds too much water: it takes far longer to dry out and tends to go leathery rather than crisp. Anything stale enough that you would not want it in a sandwich is ideal here. Spread them in a single layer with space between the cubes. Piled up, they steam each other and the ones in the middle stay soft. They also finish crisping as they cool, so a crouton that seems slightly soft coming out of the oven is usually fine five minutes later. Both the butter and the garlic are marked optional in the recipe, and that is genuine: plain cubes of bread dried in the oven are still croutons. Herbs can replace the garlic. Stored airtight, they keep for a week.