Preheat the oven to 350°F (175°C). In a mixing bowl, combine flour, sugar, and cold butter. Mix until crumbly. Add egg yolk and mix until dough forms.

Press the dough into a tart pan and bake for 15-20 minutes until golden. Let it cool.

In a bowl, mix mascarpone cheese, lemon juice, lemon zest, and sugar until smooth. Gently fold in the whipped cream.

Pour the filling into the cooled crust and refrigerate for at least 2 hours before serving.