Bolognese with butter

6 tablespoons unsalted butter 2 medium onion , finely chopped 4 celery stalks, finely chopped 4 carrots , finely chopped 3 pounds ground beef chuck (80[...]

4 tablespoons butter 4 ounces pancetta , finely chopped 2 medium carrots , finely chopped 4 medium celery ribs , peeled and finely chopped 1 medium onion ,[...]