In a cold pan, add egg yolks and sugar and whisk until fully.
Add lemon juice and zest, turn the heat on and bring to a simmer.
Cook for 5-8 mins or until the sauce thickens then turn the heat off.
Add butter (very cold from the fridge), give it a nice stir then let it rest in the fridge.
In the meantime, mix mascarpone with whipped heavy cream, icing sugar and lemon juice.
Incorporate 4 tbsps of your lemon curd and give one last mix.
Form your tiramisu alternating a layer of biscuits (soaked in milk or in a mix of water and lemon syrup) and cream.
Finish with a layer of lemon curd and rest in the fridge for at least a couple of hours, even better overnight.
