Preheat your oven to 150ºc and line the base and sides of a 20cm round cake tin with baking paper.
Place the butter, white and caramello chocolates into a large saucepan and add 200mls of water. Cook over a medium heat (stirring occasionally) until the butter and chocolate have melted and the ingredients have combined. Set aside for 5 minutes to cool slightly.
Meanwhile, transfer the Caramel Top n Fill into a small bowl and whisk until it’s a smooth consistency. Add ¾ of the Top n Fill (approximately 200g) to the saucepan with the melted ingredients, as well as the brown sugar and vanilla and whisk to combine. Alternatively you can transfer all of the ingredients to the bowl of an electric mixer if you prefer not to combine them by hand.
Add the eggs to the chocolate mixture and mix to combine. Then add the sifted flours and whisk until the mixture is smooth.
Pour the mixture into cake tin you prepared earlier and cook for 1hr and 15 mins, or until a skewer inserted into the middle comes out with moist crumbs on it.
Once the cake has cooled completely top it with the remaining Caramel Top & Fill and decorate with caramel popcorn.