Combine the vodka, rosemary, fresh grape juice and ice in a cocktail shaker and shake hard. Strain into a martini glass. Thread 1 grape on a rosemary sprig and place in glass. Serve.
*To make fresh grape juice, purée 1 cup seedless green California grapes in a food processor or blender and strain through a fine sieve. It will make about 1/3 cup.