Mashed Potatoes Au Gratin (serves 6 - 8)

I love potato salad, but have you ever thought of taking it one step further?  Try this recipe, it will be a pleasant surprise. 

6 cups cooked potatoes
1/2 cup mayonnaise
2 tbsp prepared mustard
2 tbsp white vinegar
1 medium chopped onion
1/2 cup shredded cheese

Mash your cooked potatoes with a little milk until smooth.  Add all the ingredients except for the cheese & put in baking casserole dish.  Top with the cheese & bake at 350 degrees for 15 minutes or until the cheese is melted.