Preheat oven to 200 C / Gas 6. Line a springform tin (25cm in diameter) with baking parchment.
Knead the flour with 125g butter, 75g sugar and the egg into a pastry. Roll the pastry on a lightly floured work surface and line the springform tin with it. Cover with parchment and dried beans.
Bake in the preheated oven on the bottom shelf for approximately 10 minutes. Remove the beans and parchment and bake the pastry for a further 10 minutes.
Wash the limes with hot water, rub dry, and strip the peel with a zest grater into long strips and set aside. Squeeze the limes and reserve the juice.
Add the lime juice with half the orange juice, 125g butter and 275g sugar to a saucepan and bring to the boil. Reduce heat. Mix the remaining orange juice with the cornflour until smooth and thicken the lime juice mixture with it.
Mix the egg yolks with a little lime juice mixture. Stirring constantly, mix in the remaining lime juice mixture. Pour immediately over the cooked pastry base and leave to chill.
Stir the mascarpone in a bowl until smooth. Beat the cream with icing sugar and vanilla until stiff and fold into the mascarpone. Spread over the cooled creme. Decorate the tart with lime strips. Chill for at least two hours in the refrigerator.