For the dough, mix together the flour, sugar, cocoa powder, salt and vanilla. Add the cold butter in pieces and water and knead into a dough as quickly as possible. Gradually add a little more water if necessary. Shape the dough into a ball, cover or wrap in cling film and chill in the fridge for at least 60 minutes (or overnight).

Preheat the oven to 180 degrees Celsius. Take the dough out of the fridge - if it has been chilled overnight, allow it to come up to temperature for approx. 15 - 20 minutes - and roll out to a thickness of approx. 2-3 mm on a well-floured work surface. Then cut out as many tops (with a ‘hole’ in the centre) as bottoms from the dough.

Carefully place each one on a baking tray lined with baking paper and bake in the oven for approx. 12 - 15 minutes. Remove from the oven and leave to cool.

Bring the jam to the boil in a pan to make it more liquid. Place a dollop of jam on the underside of each biscuit, place one top side on top and press down carefully. Leave to dry.

Melt the chocolate. Coat half of the top of each biscuit with chocolate and sprinkle with chocolate chips or sprinkles. Leave to dry again and store in an airtight box.