Pat the ribs dry with paper towels. Remove the membrane from the back of the ribs if not already done. Season both sides generously with salt, black pepper, and garlic powder.

In a bowl, whisk together 0.5 cup soy sauce, 0.25 cup brown sugar, rice vinegar, sesame oil, minced garlic, grated ginger, and red pepper flakes (if using). This is your initial marinade and glaze base. Reserve about half of this mixture in a separate bowl for later use as a basting sauce. The remaining half will be used to marinate the ribs.

Place the seasoned ribs in a large baking dish or a large zip-top bag. Pour the marinade over the ribs, ensuring they are well coated. Marinate in the refrigerator for at least 30 minutes, or up to 4 hours for deeper flavor.

Preheat oven to 275°F (135°C). Remove ribs from marinade (discard marinade that touched raw meat). Wrap the ribs tightly in aluminum foil. Place the foil-wrapped ribs on a baking sheet and bake for 2 hours and 30 minutes. This slow-cooking step ensures maximum tenderness.

While the ribs are slow baking, prepare the extra glaze. Take the reserved marinade mixture (the half that did not touch raw meat). In a small saucepan, combine this reserved marinade with the additional 3 tablespoons brown sugar, 2 tablespoons soy sauce, and 0.25 cup water or chicken broth. Bring to a simmer over medium heat, stirring until the sugar dissolves. If you prefer a thicker sauce, whisk 1 tablespoon of cornstarch with 1 tablespoon of cold water, then stir into the simmering sauce and cook for another minute until thickened. Set aside.

After 2 hours and 30 minutes, remove the ribs from the oven. Increase the oven temperature to 355°F (175°C). Carefully unwrap the ribs, discarding the foil and any accumulated liquid. Place the ribs directly on the baking sheet or on a rack set over a baking sheet.

Generously brush the ribs with the prepared glaze. Return to the oven and bake for 15 minutes. Flip the ribs, brush with more glaze, and bake for another 15 minutes. Continue to brush with glaze every 5 minutes during this final step until the ribs are caramelized and sticky. For an extra crisp, you can briefly broil for 1-2 minutes, watching carefully to prevent burning.

Remove ribs from the oven and let rest for 5-10 minutes before slicing between the bones and serving. Serve with any remaining glaze on the side.