This recipe makes one drink:

Half a Granny Smith apple
3 slices of lime
20 ml elderberry flower syrup (available at for instance Ikea stores)
sparkling water.

Chop the apple finely and press together with the lime with a muddler (a bar tool used to mash liquid ingredients). Put in a shaker and add elderberry syrup and crushed ice, stir, add more ice and finally top with a bit of sparkling water. Garnish with apple slices or mint.