1Heat oven to 325°F. Grease bottom and side of shallow 2-quart casserole. Cut leeks into 1/2-inch pieces. In 3-quart saucepan, heat 2 inches water to boiling. Add leeks. Cover and cook over medium heat about 5 minutes or until crisp-tender; drain.
2In 2-quart saucepan, melt 2 tablespoons butter over low heat. Cook flour, salt and pepper over low heat, stirring constantly, until smooth and bubbly; remove from heat. Gradually stir in milk. Heat to boiling, stirring constantly. Boil and stir 1 minute. Stir in cheese until melted. Stir in leeks. Pour into casserole.
3In small bowl, mix bread crumbs and 2 teaspoons butter until crumbly. Sprinkle evenly over casserole.
4Bake uncovered about 25 minutes or until golden brown.