Slow Cooker Beefy French Onion Soup

lbs. short ribs

kosher salt

sprigs fresh tarragon

peppercorns

dried parsley

dried thyme

carrots, peeled and cut into large pieces

medium onions, peeled and quartered

celery stalks, cut into large pieces

water

medium to large onions, peeled, cut in half and sliced

butter plus 1 tablespoon olive oil

salt

dried thyme

marsala wine

gruyere cheese, shredded (if you like the whole bowl covered with cheese you'll need 6 cups)

french baguette, sliced and lightly toasted (you'll need 2 pieces for each bowl of soup)