Make the sauce, then split it in half this is the step that saves the glaze: In a bowl, whisk together the soy sauce, pineapple juice, brown sugar, garlic, ginger, and sesame oil. Divide the sauce into two separate containers before it ever touches raw chicken one half becomes the marinade, and the other becomes a glaze you’ll cook down separately later.
Marinate the chicken: Pour one half of the sauce over the chicken thighs in a bowl or zip-top bag, and refrigerate for at least 2 hours, or up to overnight for deeper flavor.
Reduce the reserved half into a glaze do this before grilling: In a small saucepan, bring the second, un-touched half of the sauce to a simmer over medium heat. Whisk in the cornstarch slurry and cook for 1–2 minutes, until it thickens and turns glossy. Set aside. Using this separately reduced glaze instead of brushing the chicken with the same sauce it marinated in is what lets you build a genuinely sticky coating without either burning the sugar too early on the grill or risking cross-contamination from the raw marinade most homemade teriyaki either burns from too much sauce on the grill from the start, or ends up thin and un-clingy because there’s no reduced glaze at all.
Preheat the grill to medium-high heat, around 400°F, and lightly oil the grates.
Grill the chicken: Remove the chicken from the marinade, letting excess drip off, and discard the used marinade. Grill for 6–7 minutes per side, until the internal temperature reaches 165°F and grill marks have formed.
Brush with the glaze in the final minutes: During the last 2–3 minutes of grilling, brush both sides of the chicken generously with the reduced glaze, letting it caramelize slightly against the direct heat without burning. Pro tip: if you’re also grilling pineapple rings, add them during this same window they only need 2–3 minutes per side to pick up good grill marks.
Rest and serve: Let the chicken rest for 5 minutes before slicing or serving whole. Top with green onions and sesame seeds, and serve.
