• Line the sides of an 8-inch (20 cm) square springform pan with acetate sheets.
• Have the ladyfingers ready, trimming them as needed to fit the pan perfectly.

Prepare the lemon sugar syrup.

• In a saucepan add the water, sugar lemon zest and lemon juice.
  
• Boil for 3 minutes.
  
• Set aside to cool.
  

Prepare the blueberry sauce.

• Add the blueberries, sugar, lemon juice to a small saucepan.
  
• Cook over medium heat for about 5 minutes, stirring occasionally, until the blueberries begin to soften and release their juices. Lightly mash some of the berries with the back of a spoon.
  
• Stir the cornstarch with the water to make a slurry, then add it to the saucepan.
  
• Cook for another 1–2 minutes, stirring constantly, until thickened.
  
• Remove from the heat and let cool completely.
  

Prepare the mascarpone filling.

• In a large bowl mix Mascarpone cheese with powdered sugar, lemon zest and vanilla extract.
  
• Add whipping cream.
  
• Continue mixing until stiff peaks form.
  

Assemble the blueberry Tiramisu

• Dip ladyfingers in the lemon sugar syrup and arrange in a single layer in the pan.
  
• Spread a third of Mascarpone mixture over the ladyfingers. Use an offset spatula to spread evenly.
  
• Gently spread more than a half of the blueberry sauce.
  
• Cover with another third of Mascarpone mixture.
  
• Use an offset spatula to spread evenly.
  
• Dip the remaining ladyfingers into the lemon sugar syrup and arrange another layer of ladyfingers on top of the Mascarpone mixture.
  
• Spread the remaining Mascarpone mixture on top of the ladyfingers.
  
• Spoon the remaining blueberry sauce on top.
  
• Use a skewer to create swirls.
  
• Cover and refrigerate for at least 4 hours or overnight.
  
• Decorate with fresh blueberries and lemon slices.
  
• Slice and enjoy! Keep the leftovers refrigerated.