Sweet Potato Gratin – Fustini's Oils & Vinegars

Ingredients

• 3 tablespoons Fustini's Herbs de Provence olive oil, divided, plus more for foil
• 1 tablespoon garlic clove, chopped
• 2 tablespoons chopped fresh thyme leaves, plus more for serving
• 1 tablespoon chopped fresh sage leaves
• Kosher salt
• 1 cup heavy cream
• 3/4 cup whole milk
• 1/4 teaspoon ground cinnamon
• 1/4 teaspoon ground nutmeg
• 2 large eggs
• 3/4 cup grated Parmesan (about 2 oz.), divided
• Freshly ground black pepper
• 2 lb. sweet potatoes, peeled and sliced 1/8" thick
• 2 2/3 cup shredded Gruyère cheese (about 8 1/2 oz.), divided