Preparation

Make the yurinchi tare

• In a small bowl, whisk the vinegar, scallion, soy sauce, oil, and ginger. Set aside.

Make the chicken

• Whisk the starch and flour in a small bowl, and set aside.
• Pierce the chicken all over with a paring knife, cut into 1-1/2- to 2-inch pieces, and transfer to a medium bowl. Massage the following ingredients into the chicken one at a time in this order: 1 Tbs. salt and 1 Tbs. pepper, the garlic, ginger, sugar, papaya, if using, sake, mirin, soy sauce, and egg. Add 1 Tbs. of the flour mixture, continuing to massage until incorporated. Add the sesame oil and mix well. Use immediately, or cover and refrigerate for up to 2 hours. Drain the excess marinade, and lightly pat the chicken dry with paper towels.
• Position a rack over a large rimmed baking sheet and set aside. Pour the oil into a large Dutch oven or other heavy-duty pot until two-thirds full.
• Heat the oil to 310°F. Lightly coat a few pieces of chicken in the remaining flour mixture, shaking off any excess. Pinch the edges of each piece of chicken together to form a pouch, skin side out. Drop into the oil and fry in batches until light golden-brown, about 3 minutes. Remove from the oil with a slotted spoon and transfer to the prepared rack. Repeat with the remaining chicken.
• Once all the chicken has been fried, increase the oil temperature to 370°F. Fry the chicken a second time in batches until deep golden and crisp, about 1 minute. Return the chicken to the rack. Serve with the Yurinchi Tare.