- Thinly slice the onion and the celery.
- Saute the onion, celery and mushrooms over medium heat with either butter, lard or olive oil until translucent.
- Finely dice the cheeses.
- Drain the green beans and pour into a greased casserole dish.
- Add the sauteed vegetables, cream, and mayo, stir to combine.
- Add salt and pepper to taste.
- Add in the cheese and do a final mix.
- Cook at 350F for 35 minutes.