Step 1

Sprinkle ribs with 1/2 teaspoon salt and pepper. Heat 1 tablespoon oil in a large skillet over medium-high heat. Add the ribs and cook until browned on all sides, about 5 minutes total. Transfer to a 6-quart or larger slow cooker.

Step 2

Add the remaining 1 tablespoon oil and onion to the pan; cook, stirring occasionally, until starting to brown, 3 to 5 minutes. Stir in tomato paste, garlic and thyme; cook, stirring, for 1 minute. Add vinegar and cook, scraping up any browned bits, until the liquid is mostly reduced, 3 to 5 minutes. Transfer to the slow cooker and add broth. Cover and cook on High for 4 hours or Low for 8 hours.

Step 3

Transfer the ribs to a serving platter. Transfer the liquid to a medium saucepan and bring to a boil over high heat. Whisk cornstarch and water in a small bowl and add to the boiling liquid. Cook, whisking, until thickened, about 2 minutes. Stir in the remaining 1/4 teaspoon salt. Serve the ribs with the gravy and sprinkled with parsley, if desired.