Blend sugar with 2 ½ cup of water. Bring to a boil and poach until sugar completely dissolved. Add cored tangerines, bring to a boil and simmer for 10 minutes. Cool.
Take off fruits. Go on simmering the syrup until it cooked down to 1 1/5 cup. Cool and add liqueur.
Put tangerines in a ramekin, cover with the prepared syrup and top with mint leaves.
Master’s Advise
It would be better to use orange liqueur, for instance brandy with orange (so-called grand marnier), and colorless distillate with alcohol (contre)