Preheat an oven to 180°C.
Beat the flour, butter, sugar and vanilla together for the biscuits until combined. Roll small amounts into thin sausages, then lay on a baking tray, well spaced apart. Bake for 10 minutes until golden and crisp.
Pour the milk into a pan and heat until almost boiling. Mix the icing sugar, cocoa powder, cornflour and instant coffee. Whisk into the milk. Stir for 2 minutes until evenly combined, bubbling and thickened.
Remove from the heat, break up the dark chocolate and add to the hot mix with the nutella.
Pour the hot chocolate into mugs and serve with a biscuit or two to dunk and the frozen cream swirls for people to add their own. Serves 4