Heat fresh broccoli in a deep, 2 1/2-quart, heat-resistant, non-metallic casserole, covered, in Microwave Oven 8 to 9 minutes. (Note: If frozen broccoli spears are used, defrost and place in a shallow, 9-inch, heat-resistant, non-metallic baking dish.)
In a small, heat-resistant, non-metallic bowl, combine butter, mushrooms and onion. Heat, uncovered, in Microwave Oven 3 minutes. Stir occasionally.
Blend flour and seasonings into butter-mushroom mixture. Heat, uncovered, in Microwave Oven 3 minutes, stirring after 1 1/2 minutes.
Gradually add milk, stirring until mixture is smooth. Heat, uncovered, in Microwave Oven 3 minutes. Stir every minute.
Pour hot mushroom sauce over cooked broccoli. Sprinkle with 1 cup cheese and paprika. Heat, uncovered, 4 to 5 minutes or until cheese is melted.