Make-Ahead Roasted Root Veggie Casserole - Food Gardening Network

Ingredients

• 1 celery root, peeled
• 3 parsnips, peeled
• 1 large sweet potato, unpeeled
• 2 to 3 russet potatoes, unpeeled
• 1 red onion
• 1 tablespoon olive oil
• 1 tablespoon fresh thyme leaves
• 1 teaspoon salt
• 1/2 teaspoon freshly ground black pepper
• 2 tablespoons unsalted butter
• 3 garlic cloves, slivered
• 3 cups heavy cream
• 2 bay leaves
• 1 cup shredded cheddar cheese
• 1/2 cup grated Parmesan cheese
• Rosemary sprigs, for garnish