Cook the blueberry compote

• Combine the blueberries, water, sugar and lemon juice in a saucepan.
• Cook over medium heat, stirring, until the blueberries burst and the mixture thickens slightly.
• Set aside to cool completely.

Make the blueberry curd

• Whisk the blueberry jam, water, cornstarch, egg and lemon juice in a saucepan until smooth.
• Cook over low heat, whisking constantly, until the curd thickens.
• Remove from the heat and let cool.

Whip the mascarpone cream

• Whip the heavy cream with the sugar and vanilla extract to soft peaks.
• Fold in the mascarpone gently until smooth and creamy.

Soak the ladyfingers

• Mix some of the cooled blueberry compote with a little water to make a soaking liquid.
• Dip each ladyfinger briefly into the blueberry liquid.

Assemble the tiramisu

• Layer the soaked ladyfingers in the bottom of the dish.
• Spread over half of the mascarpone cream, then a layer of blueberry compote.
• Repeat with the remaining ladyfingers, cream and compote.

Top and chill

• Spread the blueberry curd over the top of the tiramisu.
• Refrigerate until set before serving.