Make the tart by first crushing the biscuits into fine crumbs. Add the butter to the mixture and press it into a tart pan. It should be frozen for around an hour.
This will give you plenty of time to make lemon curd or whip up the mascarpone. Combine all ingredients in a heatproof bowl. Heat the water to simmer. Whisk them until they become thick and glossy. Now It should be sifted through a fine sieve.
After this, Cover it with plastic wrap, and let it cool in the fridge until it is ready to use. Whip the whipping cream and then add the mascarpone. Continue whipping for a minute or two.
After both ingredients are combined, let it cool down a bit before you combine them. To create a marble effect, fill the biscuits with mascarpone cream. Top it with lemon curd. Now You can serve it immediately, or let it chill for a creamier consistency.