First, make the jam. Put the raspberries in a small pan and crush completely using a potato masher or fork. Add the sugar and stir until combined. Put the pan over a low heat, stirring until the sugar has dissolved, about 5 mins. Turn up the heat to medium-high and boil for a further 5 mins until slightly thickened. Remove from the heat, then pass through a sieve over a bowl to remove the raspberry seeds. Cover and leave the jam to cool to room temperature and then put in the fridge to set.

Meanwhile, make the biscuit. Beat the butter and sugar in a bowl for around 5 mins using a wooden spoon or stand mixer fitted with the whisk attachment until slightly fluffy and pale. Add the egg and beat until just combined. Add the flour, cornflour, vanilla and 1/2 tsp salt, and beat until the dough is smooth and comes together.

Roll the dough out between two pieces of baking parchment until it's about 8mm thick. Chill in the fridge for 30 mins to firm up.

Cut out two large circles (about 15cm) from the dough using a large ring cutter or bowl as a guide. Stamp out the centre of one of the circles using a heart-shaped cutter. Put the dough back in the fridge and to chill for a further 10 mins. Heat the oven to 180C/160C fan/gas 4.

Bake for 14-16 mins until the edges begin to turn slightly golden. Remove from the oven and dust with some caster sugar while still warm. Leave to cool on a wire rack. Spoon the jam onto the whole biscuit and sandwich it with the other cut-out piece. Will keep in an airtight container for two days.