Preheat oven to 375°F (191°C). Line a large baking sheet with parchment paper or a silicone baking mat.

Tear or slice bread into small bite-size pieces and place them in a large bowl. You should have around 6 to 8 cups of bread cubes, give or take.

In a small saucepan over medium heat, whisk together olive oil, butter, Italian seasoning, parsley, garlic powder, salt, and pepper until the butter is melted and everything is combined, about 3–5 minutes. Pour over the bread cubes, add the optional parmesan cheese, and stir/toss until all the pieces of bread are coated. Spread the seasoned bread cubes in a single layer on the prepared baking sheet.

Bake for 10 minutes, remove from the oven and stir, then return the pan to the oven and bake for an additional 8 minutes. Remove from the oven and set the baking sheet on a cooling rack. Let the croutons cool on the baking sheet for 30 minutes; they will continue to crisp up as they cool.

Store leftover croutons lightly covered at room temperature for up to 1 day; after that, store covered tightly for up to 10 days.