Select the raspberries and wash them briefly if necessary. Squeeze the lime and put 2 tbsp. juice aside.
Dip the edge of the glass into the remaining lime juice. Drain a little, then turn in the brown sugar and let it dry.
Halve the avocado, stone it and remove the flesh. Cut the avocado roughly. Puree avocado, raspberries and 2 tbsp. lime juice. Stir in kefir. Season to taste with salt. Pour into the glasses and garnish with lemon balm.