8 beef short ribs
extra-virgin olive oil
kosher salt and freshly ground black pepper
2 tablespoons unsalted butter
2 cups diced onion
2 cups diced celery
2 cups diced carrots
2 cups diced mushrooms
4 garlic cloves, minced
1 tablespoon tomato paste
one 750-ml bottle Cabernet Sauvignon (or other dry red wine)
1 sprig fresh rosemary
3 bay leaves
4 cups beef stock
1 tablespoon corn starch mixed with 1 tablespoon cold water