In a mixing bowl, combine the heavy cream, mascarpone, lemon curd, and sugar. Beat until smooth and thick.
Fill a small bowl with diluted blueberry syrup or cassis. Dip the ladyfingers into the liquid and use them to cover the bottom of your dish.
Spread just under half of the mascarpone mixture over the ladyfingers. Scatter some blueberries on top and add a thin layer of mascarpone filling over them. Be sure to save about half of the mixture for the top layer.
Dip another layer of ladyfingers into the syrup, then spread with the remaining mascarpone mixture. Cover the entire top with blueberries. Place the tiramisu in the fridge for at least 1 hour to set.
Remove from the fridge and cut into 9 even pieces. Dust with powdered sugar before serving.
How to store
Keep covered in the refrigerator for max 3-4 days.