For the crouton topping: Adjust oven rack to middle position and preheat oven to 400°F.
Place the bread cubes on a baking sheet and season the bread with salt, pepper and EVOO. Toast in the oven until golden brown, about 5 minutes.
Let croutons cool and reserve them for when you need them. The crouton topping can be made up to one week ahead. Store in an air-tight container until ready to use.
For the casserole: Adjust oven rack to middle position and preheat oven to 400°F.
Place the sweet potato chunks on a large baking sheet and season them with salt, pepper and a drizzle of EVOO. Roast them for about 45 minutes, or until tender.
Butter a 9x13” casserole dish and set aside.