In large saucepan melt 2 tablespoons butter. Stir in flour, salt and paprika. Add milk and mustard. Cook, stirring frequently, over medium-high heat until mixture boils and thickens. Cook and stir for 1 minute more. Remove from heat. Stir in cheese, one-fourth at a time, until melted.
In greased 8 x 8 x 2-inch baking dish layer rice, broccoli, tuna and cheese mixture.
In small bowl toss together cereal and 1 teaspoon butter. Sprinkle over top of cheese. Bake, uncovered, at 400°F about 18 minutes or until heated through and bubbly around edges.