Mix yogurt with chia seeds, vanilla sugar, vanilla pulp and rum flavoring.
Then pour into 4 dessert glasses, cover with plastic wrap and refrigerate overnight.
The next day, puree the blueberries with powdered sugar (setting aside a few handfuls of berries for garnish). Pour the puree into a saucepan, bring to a gentle simmer and thicken with 1 tablespoon dissolved cornstarch. Allow to cool slightly.
Then divide among the 4 dessert glasses, cover them again with plastic wrap and refrigerate again.
Shortly before serving, sprinkle with whipped cream, blueberries and chocolate shavings.