Scalloped Sweet Potatoes

Place sweet potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until almost tender, about 15 minutes.

Meanwhile, melt 2 tablespoons butter in a large saucepan over medium heat. Add leek; cover and and cook, stirring occasionally, until tender, about 7 minutes. Stir in flour, salt, and pepper; cook, stirring for 1 minute. Stir in milk slowly. Cook, stirring, until evenly thickened, about 5 minutes.

Remove sauce from heat. Drain sweet potatoes and gently stir in sauce to coat. Arrange potatoes in rows in an 8-inch square glass baking dish. Spoon any remaining sauce on top.

Stir bread crumbs, Parmesan cheese, and butter for topping together in a small bowl until crumbly. Sprinkle over sweet potatoes.

Bake, uncovered, until heated through, about 20 minutes. Turn on the oven's broiler and broil until golden, about 3 minutes.