Chili Con Queso

In frying pan, saute onions in butter until tender. Do not brown. Stir in tomatoes, chili peppers and salt. Simmer for 15 minutes. Cube cheddar cheese. Add cheese a few pieces at a time into frying pan. Stir until all the cheese is melted. Pour into chafing dish or fondue pot. Keep warm. Serve with corn chips. Thin mixture with milk if thick.