Cookin’ with Carolyn Absolutely Delicious Green Bean Casserole

Absolutely Delicious Green Bean Casserole
3 cups water
3/4 tsp. salt
3 (12-oz.) pkgs. 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 Tbsp. flour
3/4 cup milk
2 Tbsp. chopped fresh parsley
3/4 tsp. lemon zest
1/4 tsp. black pepper
1-1/2 cups sour cream
3/4 cup shredded cheddar cheese (2-1/2 oz.)
1 (6 oz.) can French-fried onions
Preheat oven to 350 degrees. Combine water and 1/2 tsp. salt in a saucepan. Add green beans. Bring to a boil, covered, over medium-high heat and cook beans until tender but still bright green, about 5 min. Drain well. Melt butter in a large skillet over medium heat. Cook onion and mushrooms, stirring occasionally, until tender, 5-7 min. Sprinkle with flour and cook, stirring, 1 min. Stir in milk and cook until mixture is smooth and bubbling, about 2 min. Stir in parsley, lemon zest, pepper, and remaining 1/4 tsp. salt. Remove from heat and stir in sour cream, 1/2 cup cheese, and 1/2 cup cheese, and 1/2 cup French-fried onions. Stir in green beans and transfer to a 2-1/2- to 3 quart casserole or baking dish Sprinkle with remaining 1/4 cup cheese and 1/2 cup French-fried onions. Bake until cheese melts and casserole is hot, about 20 min.