In A Large Skillet, Cook Beef And Onion Over Medium Heat Until Meat Is No Longer Pink; Drain. Stir In Tomato Sauce And Spaghetti Sauce Mix. Reduce Heat; Simmer, Uncovered, For 5 Minutes. Remove From The Heat; Stir In Sour Cream. Spoon Into A Greased 13-In. X 9-In. X 2-In. Baking Dish. Sprinkle With Mozzarella Cheese. Unroll Crescent Dough Into One Rectangle; Seal Seams And Perforations. Place Over Cheese. Brush With Butter And Sprinkle With Parmesan Cheese. Bake, Uncovered, At 375 Degrees F For 25-30 Minutes Or Until Golden Brown.