In a heatproof bowl set over a pan of simmering water, whisk egg yolks and caster sugar until pale, thick and doubled in volume, about 8-10 minutes. Remove from heat and let cool for 5 minutes.

Add the mascarpone cheese and vanilla extract to the egg mixture, whisking until smooth and well combined.

In a separate bowl, whip the double cream to soft peaks, then gently fold into the mascarpone mixture along with the zest of 2 lemons.

Combine the lemon juice, limoncello, and water in a shallow dish to create the soaking liquid.

Quickly dip each ladyfinger into the lemon mixture, ensuring they are moistened but not soggy, and arrange in a single layer in a 20x25cm dish.

Spread half of the mascarpone cream evenly over the ladyfingers, then repeat with another layer of dipped ladyfingers and remaining cream.

Cover with cling film and refrigerate for at least 4 hours, or overnight for best results.

Before serving, dust with icing sugar, sprinkle with remaining lemon zest, and garnish with fresh mint leaves.