- 5 tablespoons unsalted butter
- 1 large onion, chopped (about 2 cups)
- 1/2 cup all-purpose flour
- 2 cups whole milk
- 1 tablespoon fresh rosemary leaves, chopped
- 1 teaspoon kosher salt
- freshly ground black pepper
- 3 large sweet potatoes, peeled and shredded (about 4 1/2 cups)
- 2 cups Cheddar, shredded (8 ounces)
- 1 slice whole-wheat bread, ground in a food processor (1/2 cup)
- Heat oven to 400º F.
- Lightly coat a 9-inch square baking dish with vegetable cooking spray.
- In a medium saucepan, over medium heat, melt the butter and add the onion; cook until softened, about 10 minutes. Remove from heat, stir in the flour, then whisk in the milk, rosemary, salt, and a few grinds of pepper. Heat to boiling, whisking constantly. Stir in the sweet potatoes.
- Transfer to the baking dish and sprinkle with the Cheddar and bread crumbs. Bake for 30 minutes or until golden.