Trim excess fat from the beef short ribs, pat dry, and season generously with salt and pepper.

Sear the seasoned ribs in a hot skillet with a splash of oil for 3-4 minutes per side until golden brown.

Combine soy sauce, hoisin sauce, mirin, brown sugar, minced garlic, and grated ginger in a bowl and whisk until smooth.

Layer the seared ribs in a Dutch oven or roasting pan, add sliced onions and green onions, and cover with marinade. Cover and roast at 275-300°F for 3-4 hours.

Remove ribs and bring the braising liquid to a simmer, then let it reduce until thick and glossy, adjusting with cornstarch slurry if necessary.

Optionally, broil the ribs brushed with reduced glaze for 2-3 minutes until caramelized.

Serve ribs over steamed jasmine rice or sautéed vegetables, drizzle with glaze, and garnish with green onions.