Put raspberries, lime juice, 2 tablespoons of vodka and jam sugar in a pot and mix. Let simmer for 4-5 minutes while stirring. Pour half of the jam into a clean small glass with twist-off lid and close it immediately. Put it on the lid for about 5 minutes, turn it over and let it cool down. Spread the rest of the jam on the two glasses and let it cool down.
Halve the grapefruits and squeeze the juice. Rinse limes hot and cut into slices. Put the rest of the vodka, grapefruit juice and cranberry juice in a shaker and mix well. Pour ice into the glasses and fill up with the juice mix. Garnish with lime wedges.