The BEST Green Bean Casserole

Bahan-bahan (8 porsi)

• 2 pounds fresh green beans, trimmed and cut into bite-sized pieces
• 1 batch Mushroom Alfredo Sauce (see below)
• 1 batch Crispy Onion Topping (see below)
• 1 tablespoon butter or olive oil, divided
• 1 medium red onion, peeled and thinly-sliced
• 1/2 cup Panko breadcrumbs
• 1/4 cup freshly-grated Parmesan cheese
• 1/4 teaspoon each fine sea salt and freshly-cracked black pepper
• 2 tablespoons butter or olive oil
• 8 ounces baby bella mushrooms, thinly sliced
• 4 cloves garlic, pressed or minced
• 3 tablespoons all-purpose flour
• 1/2 cup vegetable stock
• 1 cup milk (I used 2%, but any milk will do)
• 1/2 cup freshly-grated Parmesan cheese
• 1/2 teaspoon fine sea salt
• 1/4 teaspoon freshly-ground black pepper