Pat the short ribs dry with paper towels. Rub with avocado oil and season evenly with salt and black pepper.
4 large (2 lbs / 907 g) bone-in beef short ribs, 1 tbsp (15 ml) avocado oil, ½ tsp (3 g) fine sea salt, ½ tsp (1 g) ground black pepper
Heat a large, heavy skillet over medium-high heat. Sear the short ribs for 2–3 minutes per side, working in batches if necessary, until well browned on all sides. Transfer the ribs to the slow cooker.
In a large mixing bowl, whisk together the brown sugar, ginger, garlic, gochujang, toasted sesame oil, soy sauce, beef stock, and mirin until the sugar dissolves and the gochujang is evenly distributed.
⅓ cup (70 g) packed light brown sugar, 2 tbsps (12 g) finely grated fresh ginger, ¼ cup minced fresh garlic, 3 tbsps (48 g) Gochujang (Korean chili paste), 1 tsp (5 ml) toasted sesame oil, ½ cup (120 ml) low sodium soy sauce, 4 cups (960 ml) low-sodium beef stock
Arrange the sliced onions around the short ribs in the slow cooker. Pour the braising liquid over the beef and onions. Cover and cook on LOW for 8–10 hours or HIGH for 4–6 hours, until the short ribs are fork-tender and the meat separates easily from the bone. If the ribs are still firm, continue cooking and check again after 30–60 minutes.
1 cup (160 g) thinly sliced yellow onion
Carefully transfer the short ribs to a serving dish. Skim excess fat from the cooking liquid, then transfer the liquid and softened onions to a large saucepan.
Bring the cooking liquid to a simmer over medium heat. In a small bowl, whisk 2 tablespoons (16 g) cornstarch with 2 tablespoons (30 mL) cold water until smooth. Slowly whisk the slurry into the simmering liquid. Cook for 2–3 minutes, stirring frequently, until the sauce begins to thicken.
2 tbsps (16 g) cornstarch, 2 tbsps (30 ml) cold water
For a thicker sauce, mix additional cornstarch with an equal volume of cold water and gradually whisk it into the simmering liquid, allowing the sauce to thicken between additions. Use no more than 4 tablespoons (32 g) cornstarch total. The finished sauce should lightly coat a spoon while remaining pourable. Taste and adjust the seasoning or gochujang as desired.
Spoon the sauce and softened onions over the short ribs. Garnish with chopped green onions and sesame seeds. Serve warm over steamed rice, with kimchi or vegetables on the side, if desired.
2-3 green onions, 1 tbsp (9 g) sesame seeds