3 c water
3/4 t salt
3 (12 oz.) packages frozen French cut green beans
1/2 stick butter
1 medium onion, halved and thinly sliced
12 oz. cremini mushrooms, trimmed and quartered (about 3 cups)
3 T flour
3/4 c milk
2 T chopped fresh parsley
3/4 t lemon zest
1/4 t black pepper
1 1/2 c sour cream
3/4 c shredded cheddar cheese (2 1/2 ounce)
1 (6 oz.) can French-fried onions
1 Preheat oven to 350º
2 Combine water and 1/2 t salt in a saucepan. Add green beans. Bring to a boil, covered, oven medium-high heat and cook beans until tender but still bright green, about 5 minutes. Drain well.
3 Melt butter in a large skillet oven medium heat. Cook onion and mushrooms, stirring occasionally, until tender, 5 to 7 minutes. Sprinkle with flour and cook, stirring 1 minute. Stir in mild and cook until mixture is smooth and bubbling, about 2 minutes. Stir in parsley, lemon zest, pepper, and remaining 1/4 t salt.
4 Remove from heat and stir in sour cream, 1/2 c cheese, and 1/2 c French-fried onions. Stir in green beans and transfer to 2 1/2 - 3 quart casserole or baking dish.
5 Sprinkle with remaining 1/4 c cheese and 1/2 c French-fried onions. Bake until cheese melts and casserole is hot, about 20 minutes.
Per 3/4 c serving: 254 calories