• Line a large tray with baking paper and preheat your oven to 180°C (or 160°C for fan ovens).
• Place the margarine, icing sugar and vanilla extract into a large bowl then mix well until smooth.
• Sift the flour and cocoa powder into the bowl, add the milk then mix well to make a soft but thick paste. Transfer the mixture into a strong piping bag fitted with a large star nozzle.
• Pipe 2-inch swirls onto your lined tray, leaving a small space in between each one. You should end up with 18-20 swirls.
• Bake the biscuits for 10-12 minutes until firm to the touch. Let them cool on the tray for 5 minutes then carefully transfer them to a wire rack. Let them cool completely.

Ganache:

• Place the chopped chocolate into a bowl. Heat the cream in a saucepan until it's just starting to bubble at the edges then pour it over the chopped chocolate. Let it sit for 5 minutes then gently mix until smooth.
• Let the ganache cool to room temperature for 1 hour (do not refrigerate it) then use an electric whisk to whisk it up until thick and fluffy.
• Pipe or spoon the ganache onto half of the Viennese whirls and top with the other half to make 9-10 sandwiched whirls.
• Top with a dusting of icing sugar then enjoy!