Mix together the cornflour and water then combine all ingredients except chicken and sesame seeds in a small saucepan. Simmer over medium low heat, stirring, until thickened and bubbly.
Place the chicken thighs in a roasting tin and brush with the marinade. Turn the thighs and brush again.
Bake 25 minutes. Turn thighs and bake another 20-30 minutes until cooked through, brushing every 10 minutes with the marinade during cooking.