Cook blueberries with sugar on medium heat and stir until the juice runs bright. Strain through a sieve and press the pulp to catch the syrup.
Pour the warm blueberry syrup into a piping bag and set aside to cool.
Mix cream cheese, mascarpone, whipped cream stabilizer, powdered sugar, and vanilla sugar until smooth. Stream in the heavy cream and whip until firm.
Move one third of the cream to a bowl. Fold in seventy five grams of blueberry syrup.
Spoon the blueberry cream into a piping bag.
Dip Maria biscuits in milk for a blink and line a round plate with one even layer.
Pipe blueberry cream over the biscuits and smooth. Add a new biscuit layer. Pipe half of the white cream and smooth. Add a light swirl of blueberry syrup.
Repeat with another biscuit layer. Cover the sides with the rest of the white cream. Chill for a few hours or overnight for the best set.
Warm the heavy cream until it steams. Drop in white chocolate. Sit for a minute. Stir until silky and cool.
Pipe a neat band of cream around the edge. Spread the ganache in the center. Drip a little blueberry syrup on top and pull lines with a toothpick for a simple pattern. Chill again, then slice and add fresh blueberries and mint before serving.