Casa Ole Chili Con Queso

1 tbsp. butter

1/4 c. onion, minced

1-10.75 oz. can cream of celery soup

1-5 oz. can sweetened condensed milk

1-10 oz. can Retel

3 lbs. Velveeta

Saute onion in butter. Add all other ingredients and warm until melted. Serve with tortilla chips.