1 c. mayonnaise
1/2 c. sharp Cheddar cheese (grated)
1 (3 oz.) cream cheese
2 tbsp. grated onion
1/2 c. Parmesan cheese
A dash of salt and pepper if desired
1 loaf cocktail rye bread

Mix all the above together. Spread on cocktail rye bread. Broil 2 to 3 minutes or until bubbly.