Preheat the oven to 180C. Prick the duck skin all over. Slash the breast skin diagonally at intervals. Roast the duck for 1 hour.

Mix 15ml/1 tbsp soy sauce with 30ml/2 tbsp honey and brush over the duck. Sprinkle with sesame seeds. Roast for 15 minutes more.

Grate the rind from one mandarin and squeeze the juice from two. Mix in the corn flour, remaining soy sauce and honey. Heat, stirring, until thickened and clear. Season.

Peel and slice the remaining mandarins. Serve the duck with the mandarin slices and the sauce.