Sauté onions in butter until clear. Whip together eggs, whipping cream, and mayonnaise and set aside. Line pie shell with half of cheese. Add shrimp, onions and tomatoes, then remaining cheese. Add egg mixture until shell is full to the top. Mix ingredient so they are well blended. Cook at 300 degrees for about 1 hour. Quiche is done when top is golden and middle is firm.