In a bowl, mix the egg yolks, sugar, cornflour and vanilla.

Boil the milk and cream together in a saucepan.

Add the milk and cream in a thin stream to the eggs and sugar, mix until well combined.

Return the custard to a clean saucepan over a low to medium heat, stirring continuously until it comes to a boil and thickens.

Remove from the heat and transfer to a clean bowl and cover the surface with cling film to prevent a skin from forming. Allow to cool.

Preheat the oven to 180°C.

Grease the wells of a 12-hole muffin tray with butter.

Lay the puff pastry onto a clean work surface lightly dusted with flour and icing sugar. Cut the pastry in half and place one sheet on top of the other. Roll the pastry sheets up like a Swiss roll, and cut the roll into twelve slices. Lay each of the rolled pastry slices flat onto the work surface, and roll out into 10cm discs using a rolling pin.

Press a pastry disc into each of the wells of the prepared muffin tray and divide the cooled custard equally among the pastry cases.

Transfer the muffin tray to the oven and bake the tarts for 18-20 minutes or until the custard has set and is pale golden brown and the pastry is crisp and golden brown.

Allow to cool in the tin before dusting with icing sugar.