* Place half of broccoli in a steamer basket; place in a large saucepan over 1 in. of water. Bring to a boil; cover and steam for 3-4 minutes or until crisp-tender. Place in a greased 13-in. x 9-in. baking dish; repeat with remaining broccoli.
* Meanwhile, in a small saucepan over medium heat, melt 4 tablespoons butter. Add onion; cook and stir until tender. Add garlic; cook 1 minute longer.
* Stir in flour until blended; gradually add milk. Bring to a boil; cook and stir for 2 minutes or until thickened. Stir a small amount of hot mixture into egg yolk; return all to the pan, stirring constantly. Cook and stir 1 minute longer. Remove from the heat; stir in the cheese, salt and pepper.
* Pour over broccoli. In a small skillet, cook bread crumbs in remaining butter until golden brown; sprinkle over the top.
* Bake, uncovered, at 400° for 15-18 minutes or until heated through. Yield: 12 servings (3/4 cup each).