Place the first mud cake on a plate.
Top with a layer of chocolate ice-cream and add the second mud cake on top.
Working quickly, cover with the rest of the ice-cream, using a spatula to smooth as you go.
Freeze for at least 4 hours.
Just before serving, break the chocolate into pieces and melt in the microwave, stirring it every 30 seconds until nice and smooth.
Move your cake from the freezer to a cake stand, spoon the melted chocolate over the top of the cake, allowing it to drip down the sides (it will set fast against the ice-cream).
Working quickly, decorate with caramel popcorn.