Mix all ingredients in a small saucepan. Heat over medium until slightly thickened, about 15 minutes.
Start grill on medium high heat heat. Spray chicken thighs with no stick spray.
Place 1/4 cup of the sauce in a separate bowl, to start. Use more if needed. Use this to mop to chicken. Generously mop chicken on both sides.
Place on hot grill, start chicken skin side down, to crisp, and continue to mop while the chicken is cooking. Cook until chicken is cooked through, 165°F / 74°C.
Use any extra sauce to make a gravy. Mix the cornstarch with a bit of water. Pour into remaining sauce, stirring until incorporated. Let cook a few minutes, over low heat., until thickened and bubbly. Serve on the side, with potatoes, or sweet potatoes.