Preheat the oven to 180°C and grease a 20cm springform tin with butter and flour.
Mix the lemon juice and 75g sugar in a bowl until the sugar dissolves.
Whisk 200g sugar, 200g butter, and lemon zest together until pale and fluffy.
Gradually whisk in the eggs and then carefully fold in the flour.
Pour the batter into the tin and bake for 30 to 40 minutes until cooked through.
Prick the warm cake with a cocktail stick and pour the lemon drizzle over it.
Whisk egg yolks and 75g sugar in a pan over low heat until the sugar melts.
Whisk in butter, lemon juice, and zest until the mixture thickens and becomes smooth.
Fold the mascarpone into the cooled lemon curd to create a marbled effect.
Halve the cooled cake horizontally, spread the filling on the base, and replace the top.