Put the sage, sugar and salt into the bottom of the shaker. Use a muddler (or the end of a wooden spoon handle) to smash the sage up. You're not trying to puree it, but you want it really well bruised so that it releases more flavour. Half fill the shaker with ice. Add the white rum and pineapple juice, put the lid on and give it a good shake. Pour the cocktail evenly into two tall glasses with a few cubes of ice in them. Top up with sparkling mineral water and garnish with sliced pineapple, if you're feeling fancy. Put 3-4 sage leaves, 1/2 tbsp sugar and a small pinch of salt into each glass. Use a muddler (or the end of a wooden spoon handle) to smash the sage up. You're not trying to puree it, but you want it really well bruised so that it releases more flavour. To each glass, add ice, 1/8 cup (30ml) white rum and 1/4 cup (60ml) pineapple juice. Top up with sparkling mineral water and garnish with sliced pineapple, if you're feeling fancy.