Au Gratin Carrots

Source: http://www.tasteofhome.com/recipes/Au-Gratin-Carrots

Ingredients
2 pounds carrots, sliced
1/2 cup chopped onion
1/4 cup butter, divided
3 tablespoons all-purpose flour
1/2 teaspoon salt
1/8 teaspoon pepper
1-1/2 cups milk
4 ounces process American cheese, cubed
2 cups cornflakes, crushed

Cook the carrots until crisp-tender; drain and set aside. In a saucepan over medium heat, saute onion in 3 tablespoons butter until tender. Stir in flour, salt and pepper. Gradually add milk; bring to a boil, stirring constantly. Cook for 1 minute or until thickened. Stir in the cheese just until melted. Add carrots. Pour into a greased 8-in. square baking dish. Melt remaining butter; add cornflakes. Sprinkle over carrots. Bake, uncovered, at 350° for 20-25 minutes or until bubbly.