Beef and Cheese Manicotti

INGREDIENTS

• 1 (15-ounce) container whole-milk ricotta
• 3 cups marinara sauce
• 2 tablespoons chopped fresh Italian parsley leaves
• 4 teaspoons olive oil
• 3 cups shredded mozzarella
• 1 pound ground beef
• Salt and freshly ground black pepper
• 14 (8-ounce package) manicotti
• 1 medium onion, coarsely chopped
• 2 tablespoons butter, cut into pieces
• 2 garlic cloves, minced
• 1 cup grated Parmesan