Don Pablos Queso Dip

1 cup chopped onion more or less depending on how well you like onions
3 tbsp butter
2 cans (10 oz each) Rotel diced tomatoes with green chilies
1 (14 1/2 oz) can stewed tomatoes, chopped
2 lb processed cheese, such as Velveeta
1 lb sharp Cheddar cheese cubed
Corn chips, Triscuits or other

Saute onions in butter. Add tomatoes with chilies and stewed tomatoes; cook until thick. Add processed and cubed cheeses. Cook until thick and smooth, stirring often to keep from sticking. Refrigerate overnight.

Heat to eat. Serve with corn chips, Triscuits or vegetables.