3 parts rum
1 part lime juice
1 part sugar syrup

ice cubes

cocktail glass

Shake all ingredients well with some ice cubes in a shaker. Strain into a cocktail glass (the ice cubes stay in the shaker). Put a lemon slice in the glass.

If possible use fresh squeezed lime juice. There´s at least 1/2 oz. (= 1,5 cl) in each lime.