Combine mascarpone, sour cream, yoghurt, cane sugar, and vanilla sugar. Let stand for roughly 5 minutes until the sugar dissolves. Taste and adjust sweetness if desired.
Place shortbread biscuits in a freezer bag and crumble into coarse crumbs. In two glasses or bowls, layer the mascarpone mixture, then biscuit crumbs, then mascarpone mixture again. Top with fresh or frozen berries.
Melt the couverture chocolate over a water bath on medium heat. Drizzle the melted chocolate onto baking paper and place in the freezer until hardened.
If using frozen berries, refrigerate the assembled glasses or bowls for 30 minutes before serving so the berries thaw and taste fresh.