Easy Green Bean Casserole

Name: Easy Green Bean Casserole
Prep time: 10 min
Cook time: 40 min
Total time: 50 min
Cuisine: American
Ingredients: 3 tbsp butter. divided; 1/2 cup yellow onion, chopped; 8 oz fresh Bella mushrooms, sliced; 1 tbsp all-purpose flour; 2 tbsp minced garlic; 1/4 cup chicken stock; 1 cup whipping cream; 10 oz cream of mushroom soup; 1/2 cup grated Parmesan cheese; 1 cup shredded Monterey jack cheese; 1 tsp sea salt, divided; 1 tsp black pepper; 1/4 tsp ground allspice; 1/2 tsp ground thyme; 3 cans french-cut style green beans, drained; 1 1/2 cups crispy fried onions, divided