Ingredients:

1½ limes, cut into wedges
20 fresh mint leaves
2½ tsp granulated sugar
handful ice
65ml/2½fl oz white rum
splash soda water, to taste
fresh mint sprig, to garnish

Method:
 
Place the limes, mint and sugar into a sturdy highball glass and 'muddle' or mash with the end of a clean rolling pin, to bruise the mint and release the lime juice.
Add the ice and pour over the rum.
Add soda water to taste and stir well. Garnish with a mint sprig and serve.