Zest 2 of the lemons and 2 of the limes. Juice all
the fruits and keep the empty shells to serve the
granita. Tip the juice, zest, lemongrass, lime leaf
(if using), and sugar into a bowl. Pour over 500ml
boiling water. Stir everything together until the
sugar has dissolved, then leave to cool and infuse.
Strain the lemon syrup into a tray and freeze as
stated. Place the lemon and lime halves in the
freezer and fill with granita to serve.