Arrange broccoli in a steamer basket over boiling water. Cover and steam 10 minutes or just until tender. Remove from heat. Transfer broccoli to a lightly greased 2-quart gratin or other shallow baking dish.
Meanwhile, melt butter in a heavy saucepan over medium heat; add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add milk, stirring constantly. Cook, stirring constantly, until sauce is thickened and bubbly. Remove from heat; stir in mustard and next 3 ingredients. Pour sauce over broccoli; sprinkle with cheese. Broil 5 1/2" from heat 6 to 8 minutes or until lightly browned. Serve hot.