Jidori Tsukune

Tare:
1 cup sake
1 cup soy sauce
½ cup mirin (sweet Japanese rice wine)
½ cup zarame sugar or demerara sugar
Chicken and assembly:
1 lb. skin-on, boneless chicken thighs or 1 lb. ground dark-meat chicken and 2 Tbsp. chicken fat
½ small onion, finely chopped
2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt
1¾ tsp. mirin (sweet Japanese rice wine)
1½ tsp. finely grated yuzu or lemon zest
1 cup glutinous sweet rice flour
Shichimi togarashi and lemon wedges (for serving)

Tare:
Bring 1 cup sake, 1 cup soy sauce, ½ cup mirin (sweet Japanese rice wine), and ½ cup zarame sugar or demerara sugar to a boil in a medium heavy saucepan. Reduce heat and simmer, stirring occasionally, until sauce is reduced by about a quarter, 25–30 minutes.
Chicken and assembly:
If using 1 lb. skin-on, boneless chicken thighs, grind in a meat grinder fitted with a 7-mm die. Divide chicken into 2 equal portions and run 1 portion through grinder a second time. Combine both portions in a large bowl. (You can also ask your butcher to grind the chicken for you.)
If using 1 lb. ground dark-meat chicken plus 2 Tbsp. chicken fat, mix together in a large bowl.
Add ½ small onion, finely chopped, 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt, 1¾ tsp. mirin (sweet Japanese rice wine), and 1½ tsp. finely grated yuzu or lemon zest to chicken meat. Using your hands, mix until thoroughly combined.
Divide meat into ¼ cup portions. Shape into balls, then form into 3½x1" logs. Arrange tsukune on a parchment-lined baking sheet and chill until firm, about 30 minutes.
Place 1 cup glutinous sweet rice flour on a plate. Working one at a time, dredge tsukune in flour, turning to coat, and transfer as many as will snugly fit to a parchment-lined large steamer basket.
Pour water into a large saucepan to come 1" up sides and bring to a boil. Set steamer on top and cover. Steam tsukune until just cooked through, 6–8 minutes. Repeat process with any remaining tsukune if needed.
Prepare a grill for high heat. Place tare in a tall, narrow glass (you should be able to submerge tsukune when you dunk it in the tare). Thread each tsukune onto a skewer.
Grill tsukune, turning and dipping in tare every 2 minutes, until richly glazed, deeply browned, and charred in spots, about 8 minutes total.
Transfer to a platter and sprinkle shichimi togarashi over. Serve with lemon wedges for squeezing over.