For the sponge base, preheat the oven to 180C/350F/Gas 4. Grease a loose-bottomed 20cm/8in round cake tin with butter.
In a small pan, melt the rest of the butter over a gentle heat and set aside.
Place the sugar in a metal bowl and sit it over a pan of simmering water, checking that the base of the bowl is not touching the water. Break the eggs into the bowl, and with an electric hand mixer beat the mixture over the simmering water for 1-3 minutes, until it becomes pale and frothy. Remove the metal bowl from the heat and continue to beat the mixture for a further two minutes while it cools.
Gently stir in the vanilla extract and a pinch of salt. With a metal spoon, carefully fold in the sifted flour and cocoa powder. Slowly trickle in the melted butter and continue to combine gently.
Pour the mixture into the greased tin and bake for 10–12 minutes, or until the centre is firm to the touch. Remove from the oven and cool a little in the tin. Drizzle the whisky over the sponge and set aside to cool completely in the tin.
To make the honeycomb, line a 20cm/8in square cake tin with baking parchment. In a large heavy-based saucepan, heat the golden syrup and sugar together and bring to the boil, then simmer on a low heat for 5–10 minutes. The mixture will bubble and darken to a golden caramel, but be careful not to let it get too dark or the flavour will be bitter.
Stir in the cardamom and remove the pan from heat. Immediately – but carefully – add the bicarbonate of soda and mix it in; the mixture will instantly foam up significantly, which is why a large pan is needed to prepare the syrup. Pour immediately into the lined cake tin. Leave to set for at least an hour, then peel off the paper and break the honeycomb into bite-sized chunks. The honeycomb will stay crisp in a dry, airtight container for a day or two, but will gradually soften over time.
To make the chocolate torte, put the chopped chocolate into a large heatproof bowl and set aside.
Pour 200ml/7fl oz water into a pan, add the ground cardamom and sugar, and bring to the boil, stirring. When just boiling remove from the heat and cool for 30 seconds. Pour through a very fine strainer over the chocolate, stirring continuously to form a smooth glossy mixture. Discard the contents of the strainer. Stir in the whisky.
Fold the lightly whipped cream into the chocolate mixture; the mix will start to stiffen. Spoon the mixture over the cold sponge right to the edges of the cake tin, and level with a palette knife. The sponge will have shrunk away from the sides of the tin, so the torte will completely encase the sponge. Cover with cling film and chill in the fridge for a few hours, or overnight if possible.
To serve, uncover the tin and push out the torte by loosening the base and moving onto a plate. Decorate with honeycomb. Cut into slices (for a smooth, professional finish, use a knife dipped in boiling water). Decorate each slice with more pieces of honeycomb, top with edible gold dust and serve with more double cream, if you like.