Place raspberries, grand Marnier, rum, sugar, and lime juice in a blender. Blend until smooth.
Pour into 2 martini glasses and garnish with a twist of lime.
Notes
For a non-frozen version - use fresh raspberries and muddle with sugar and lime juice in a cocktail shaker. Add Grand Marnier and rum and plenty of ice and shake well, Strain into a martini glass and garnish with a lime twist or slice.