1 Large or 2 Small watermelons
250ml Lemon Juice (from a bottle or squeeze your own)
1l Bottle soda water
1 Lime, cut into slices
Small handful mint
1. Cut the top off the watermelon and hollow it out using a large spoon, fishing out any pips along the way. Mash the flesh through a sieve into a bowl. Put the flesh in a blender (or use a tall jug and hand blender) with the lemon juice and Zusto, whizz to a purée, then stir in the soda.
2. Heap some ice into the hollowed-out watermelon and fill it with the lemonade mixture. Serve the rest in a jug with the lime slices and mint. Have a bowl of extra crushed ice on the side so people can help themselves.