The sauce in this recipe is amazing! In a medium saucepan, cook onion in hot butter until onion is tender. Add garlic, salt, red pepper, and white pepper. Stir in whipping cream, Parmesan cheese, and catsup. Bring to boiling; reduce heat. Simmer, uncovered, stirring occasionally, about 15 minutes or until sauce thickens. Stir in cooked shrimp/chicken.