Crockpot Green Bean Casserole

Ingredients (14)

• FOR THE CASSEROLE:
• 2 pounds fresh green beans
• 2 tablespoons unsalted butter
• 1 medium yellow onion
• 16 ounces baby bella mushrooms
• 3 tablespoons all-purpose flour
• 2 cups whole milk
• 1 teaspoon kosher salt
• ½ teaspoon black pepper
• 1/8 teaspoon ground nutmeg
• 1 tablespoon sherry vinegar
• 1 cup shredded cheddar cheese or gruyere cheese*
• FOR THE TOPPING:
• 1 1/2 cups fried onions