To make the raspberry puree, blend thawed raspberries in a blender and push it through a sieve. DIscard the pulp.
First juice your grapefruits and gather the juice in a bowl or a glass.
Add the vodka and rosemary to a martini shaker. Muddle it well. Add some ice to the martini shaker and then the grapefruit juice and ginger.
Shake the mixture well and pour into two martini glasses.