To make the sauce, stir together the gochujang paste, soy sauce, orange juice, apple cider vinegar, sesame oil, garlic, brown sugar, and ginger until well blended. Taste and add salt if needed.
For the ribs, salt and pepper each rack on both sides. Line two sheet pans with foil, then lay out 2 (2-feet) pieces of foil and place this foil on top of the sheet pans. Place each rack on the foil, starting with the meat-side down.
Take half the sauce and then evenly spread the sauce on the racks on both sides, reserving the remaining sauce for the final glazing. With the meat-side up, wrap the ribs with the foil leaving the seam on top, then refrigerate for 4 to 8 hours.
To prepare the ribs, preheat the oven to 300°F and remove the ribs and their sheet pans from the refrigerator. Once the oven has heated, slide the ribs into the oven and cook covered for 1 hour and 40 minutes.
After this time, remove the ribs from the oven and gently open the foil and pull it back to expose the meat. The meat should be tender but if you desire it to be more so, return the ribs to the oven and continue to cook until they’re how you prefer.
Once tender, remove the ribs and turn the heat up to 450°F. Gently open the foil and pull it back to expose the meat. With tongs, flip the ribs and spread a couple of tablespoons of the remaining sauce on the bony side. Flip the ribs back over and evenly coat the meaty side with the rest of the sauce. Slide the ribs back into the oven and cook uncovered for 12-15 minutes or until the sauce is beginning to blacken.
Remove the ribs from the oven and allow to rest for 15 minutes before slicing. Garnish with sliced scallions and sesame seeds before serving.
Gochujang paste can be found at most grocery stories in either the international section or condiment section, next to soy sauce.