Prepare your glass by running a lime wedge around the rim of a martini glass. Dip the top of the glass into a plate sprinkled with sugar. In a mixing glass, muddle the raspberries with the lime juice and sugar. Add rum and lots of ice. Shake well. Pour the mixture through a sieve into a martini glass. The sieve helps catch the raspberry seeds. Garnish with a lime twist (optional). Cheers!