If you make this dip for a party, I recommend doubling the recipe. It is so addicting.
1 cup mayonnaise
1 cup chopped sweet onion
1 TBS freshly grated Parmesan cheese
1/4 tsp garlic salt
1 cup shredded Swiss cheese
In a bowl, combine mayonnaise, onion, Parmesan cheese and garlic salt; stir in Swiss cheese. Spoon into a one quart baking dish. Bake, uncovered, at 325 for 40 minutes. Serve with crackers.
Makes 2 cups
Source: Best of Country Appetizers