Mashed Potato, Rutabaga, And Parsnip Casserole With Caramelized Onions

INGREDIENTS

• 7 cups low-sodium chicken broth
• 3 pounds potatoes, peeled and cubed
• 1 1/2 pounds rutabagas, peeled and cubed
• 1 1/4 pounds parsnips, peeled and cut into 1 1/2 inch pieces
• 8 cloves garlic
• 1 bay leaf
• 1 teaspoon dried thyme
• 3/4 cup butter, softened
• 3 onions, thinly sliced
• salt to taste
• ground black pepper to taste