Oil a 20cm springform cake tin and line with cling film. Oil and line two 20cm cake tins with baking parchment. Fill the first tin with the softened cookie dough ice cream. Press it firmly into the corners and smooth the top with a palette knife. Freeze for at least 2 hrs.

Heat the oven to 180C/160C fan/gas 4. In a large bowl, whisk together the oil, eggs, buttermilk and coffee until combined. In a separate bowl, combine the sugars, cocoa powder, flour, bicarbonate of soda and baking powder either using a whisk or rubbing with your fingers, ensuring there are no lumps. Add the wet ingredients to the dry and whisk until smooth, then fold the chopped biscuits through the batter. Split the batter between the two paper-lined cake tins and bake for 25 mins, or until a skewer inserted into the middle comes out clean. Leave to cool slightly in the tin, then turn out onto a wire rack to cool completely.

Trim the top of the cakes using a bread knife to level them if they have domed. Take the ice cream out of the freezer and unwrap. Put one sponge on a cake board or plate and put the ice cream layer on top. Top with the remaining sponge and press down firmly. Transfer to a freezable container and freeze overnight.

To make the chocolate ganache topping, put the chocolate in a heatproof bowl. Pour 50ml of the cream and the golden syrup into a small saucepan over a medium heat and bring it to steaming point – don't boil it. Pour the cream mixture over the chocolate and leave to stand for 1 min. Mix together until glossy and smooth, then transfer into a squeezable bottle or piping bag and set aside to cool slightly.

Meanwhile, in a stand mixer with a whisk attachment, whip the remaining 600ml double cream with 4 tbsp icing sugar until it just holds its shape. Crumb coat the cake on the top and sides with a small amount of the cream using a palette knife to scrape the excess off and leave a thin layer. Put the cake back in the freezer for 20 mins. Use most of the remaining cream to coat the cake fully, smoothing it out with a palette knife. Put the cake back into the freezer for 30 mins to firm up.

Use a squeezable bottle or piping bag to gently line the chocolate ganache around the top edge of the cake, allowing it to drip down the sides.

Top the cake with more biscuits, ganache and any remaining cream. If it is still very frozen, leave to stand in the fridge for 5-10 mins, or return to the freezer if very soft. To serve, slice with a knife that has been run under hot water and dried.