1) Place 750ml of the tangerine juice in a medium nonreactive pan over high heat and bring to the boil. Make a few slits in 2 serranos and add them to the juice. Continue cooking until thickened and reduced to about 250ml. Remove the serranos and discard.
2) Whilst the mixture is still hot, begin adding the sugar until slightly sweet. Stir until the sugar totally dissolves.
3) Transfer the thickened juice to a large bowl. Stir in 500 to 750ml tangerine juice, zest of 2 tangerines, 2 to 3 sliced serranos, 2 to 3 tablespoons golden syrup. Allow to steep overnight, refrigerated.
4) Strain and pour into ice lolly moulds. Place in freezer until frozen.