Set aside up to 8 whole strawberries for garnish and topping. Puree the remaining strawberries until smooth. In a bowl, mix mascarpone and yogurt until smooth, then stir in vanilla sugar until combined.
Divide the mascarpone mixture equally among 4 glasses. Alternate layers of mascarpone cream and strawberry puree in each glass, starting with mascarpone and finishing with strawberry puree. Top each glass with a heaped tablespoon of mascarpone cream and place a whole strawberry on top.
Cut the reserved strawberries in half from the stem and clip one half onto the rim of each glass. Refrigerate for at least 30 minutes.
Just before serving, sprinkle with chocolate sprinkles or dust with cocoa powder, if desired.