Easy Refried Beans

4 cans fat free re-fried beans
1 - 28 to 32oz. can pinto beans or black beans (rinsed and drained)
1 stick butter
1 onion chopped

Saute onion in melted butter. Add beans, mix, and heat through. Serve with your favorite burrito items.

May place first three ingredients in crock pot on low for 2 to 3 hour. Mix and serve.