Sprinkle short ribs generously with salt and pepper on all sides.
Warm the oil in a large skillet over medium-high heat. Brown the ribs for about 2 minutes per side until a golden crust forms. Move them into the crockpot.
Arrange the sliced onion, garlic, and carrots around the meat.
Pour in the wine and broth, then stir in the tomato paste, thyme, parsley, and add the bay leaf. Cover and cook on low for 6–8 hours.
In the last hour of cooking, whisk cornstarch with the same amount of cold water in a small bowl until smooth. Stir the mixture into the crockpot, cover again, and let it finish cooking until the sauce thickens.
Serve the short ribs and vegetables over mashed potatoes. Sprinkle with herbs before serving.
Notes
You can use other steak cuts like sirloin, skirt steak, flat iron, or chuck for this recipe. Be sure to slice against the grain into strips no thicker than ½ inch.
Cooking on low produces the most tender meat. If using high heat, keep an eye on the sauce to prevent it from thickening too much or burning.
Since slow cookers vary in temperature, if the sauce is too thin at the end of cooking, transfer some to a saucepan and simmer over medium heat until it thickens. Pour it back over the beef before serving.
For firmer onions, add them halfway through the cooking time.
To increase the heat, add the dried chilis at the beginning. For more spice, try cayenne pepper, red pepper flakes, chili crisp oil, or sriracha.