Rub the rim of your cocktail glass with a wedge of lime. Add sugar to a small plate and run the rim of the cocktail glass through the sugar. Set in the refrigerator to chill.

In a cocktail shaker, add raspberries and lime juice. Muddle until the berries are broken down.

Add demerara syrup and rum. Fill shaker with ice. Shake well.

Strain through a mesh sieve into chilled cocktail glass.

Garnish with raspberries and serve.