Shepherds Pie

Name: Shepherd's Pie
Ingredients: 4 cups diced potatoes; 1/2 cup buttermilk; 3 tablespoons butter, plus 6 tablespoons butter or oil, divided; 2 tablespoons white truffle oil; 2 1/2 teaspoons kosher salt, divided; 1 1/2 teaspoons freshly ground black pepper, divided; 4 pork sausages; 1 pound ground beef; 1 teaspoon chopped rosemary leaves; 1 1/2 cups chopped carrots; 1 1/2 cups chopped celery; 3 tablespoons maple syrup; 1/2 cup grated cheese (your preference: Jack, Cheddar, or combination etc.)