How to Make It
In a medium bowl, combine the soy, dashi or water, mirin and sugar and set aside.
In a blender carafe, combine the pear, the chopped 1/2 onion, garlic and ginger. Blend until smooth. Pour the purée over the short ribs and toss to completely coat the meat. Cover with plastic and refrigerate for 30 minutes. Then pour the soy mixture over the short ribs and massage it into the meat. Cover with plastic and marinate for 3 to 4 hours.
Brush the grill or cast iron grill pan with the sesame oil and preheat over high heat. Lower the flame to medium-high once the grill or grill pan is hot. Cook the short ribs 3 to 4 minutes on each side, until caramelized and cooked to desired internal temperature.
Remove the short ribs from the grill or grill pan, and add the sliced onion and the scallions. Cook the vegetables until charred and cooked through. If using a pan, add a splash of water to deglaze. Serve the short ribs with the vegetables and deglazed pan drippings.