Pat the short ribs dry and season them all over with kosher salt, then rub on the garlic powder, onion powder, paprika, brown sugar, black pepper, and chili powder if using. The drier surface helps the spices cling and lets the meat brown instead of steam.

Heat the olive oil in a large skillet over medium-high heat and sear the ribs in batches for about 1 minute per side, or 4 to 5 minutes per batch, then transfer them to the slow cooker. Look for a deep brown crust on the outside while the center stays undercooked.

Add the sliced onion, peeled garlic cloves, and red wine to the skillet after turning off the heat, then set the pan over medium and scrape up the browned bits with a silicone spatula. A rich, fruity steam will rise, and the bottom of the pan should loosen as the onions and garlic soften over 5 minutes.

Stir the bouillon cube, Worcestershire sauce, and Dijon mustard into the skillet mixture, then pour it into the slow cooker with the beef broth, thyme, and carrots. The liquid should smell savory and balanced before the long cook begins.

Cover and cook on low for 7 to 8 hours. The ribs are ready when a fork can shred the meat with almost no pressure.

Lift out the carrots, tent them loosely with foil, and skim excess fat from the surface of the cooking liquid, then switch the slow cooker to high if needed. The broth will look clearer and less greasy once the top layer of fat is removed.

Shake the cornstarch and COLD water together in a small container until smooth. The mixture should look fully blended with no dry pockets of starch.

Stir the cornstarch slurry into the hot cooking liquid, cover, and let it thicken for 3 to 5 minutes. The sauce will stay fairly light, more like au jus than heavy gravy, but it should gain a little body.

Spoon the sauce over the short ribs and carrots when serving. Use a bowl if you want to catch every bit of that savory braising liquid.