Trim the pork ribs of any excess fat and carefully remove the membrane on the back of the ribs. Lather with mustard and season thoroughly with Sweet Teriyaki Sake seasoning. Place in the fridge for 2 hours to set.
Preheat your smoker for indirect cooking around 225F. Add some wood chips or wood chunks to the smoker for added flavor.
Add the ribs to the smoker on the indirect heat side. Cook for about 3 hours or until the outside is caramelized and a light ruby red color.
After 3 hours, pull your ribs off the smoker. Lay down a layer of aluminum foil with 3 tbsp of butter spaced out on the foil. Add some brown sugar and drizzled mirin over the butter. Top the butter mixture with one of the pork ribs with the bone side facing up. Add more butter, mirin and brown sugar on top of the rib. Carefully wrap in the foil until tight and secure. Repeat this step for all of the pork ribs.
Once done wrapping, add the ribs back to the smoker with bone side facing up. Cook for another 2 hours. About 30 minutes before the ribs are done, add a basting skillet over medium high fire. Add the sake first to reduce it by half. Next, add all the ingredients for the Sweet Teriyaki Sake BBQ Sauce to the skillet and let simmer until thickened (about 10 minutes) making sure to stir occasionally. Once done, pull off and let cool.
After 2 hours, unwrap the ribs and discard the foil. Place all the ribs back on the smoker and increase the heat to 350F. Begin glazing the outside of the ribs until with the BBQ sauce. Continue to cook the ribs for another 15-20 minutes until they are caramelized on the outside but tender on the inside.
Once done, pull the ribs off and let rest for 3-5 minutes. Serve with chopped scallions. Slice and enjoy!