I made this last night and it could not be easier!Nigella's recipe called for lemons and sparkling water- I had limes and soda water.
2 limes + 4 tablespoons sugar
750ml-1 litre soda/sparkling water
Cut each lime into eight pieces. In two batches blend 1 of the limes(8pieces) + 2 tblsp sugar + half the water. Sieve into a jug to filter out peel & pith. pour and serve with ice.
It's so quick and easy and can be adapted to cocktali recipes with a a splash of rum + mint, or gin.