Green Bean Casserole Recipe

Ingredients

• To taste kosher salt
• 3 lbs. green beans, trimmed
• 1 1/2 sticks unsalted butter, divided
• 2 yellow onions, thinly sliced
• 1 lb. cremini mushrooms, sliced
• To taste freshly ground black pepper
• 4 cloves garlic, finely chopped
• 1/2 cup all-purpose flour
• 6 cups whole milk
• 1 1/2 cups fried onions