Put sultanas in a bowl with the marmalade and the whisky and leave to soak for 1 hour.
Pre-heat the oven to 170 °C and grease a 10 inch bundt tin.
Whisk the flours together but remove 1 tablespoon of the flour and use to lightly dust inside the bundt tin, making sure to shake out the excess.
Add the baking powder and salt to the remaining flours and whisk together again. Set aside.
Cream together the butter and sugars on a low-medium setting of the food mixer until pale, light and fluffy.
Add the eggs one at a time and keep mixing until well incorporate.
Then add the 1/3 of the flour mix and beat in. Add half of the sultana/marmalade/whisky mixture and again beat in. Add the second third of the flour mix, beat, the rest of the sultana, mix, beat and then the final third of the flour mix.
Once the batter is lovely and smooth, save for the lumpy sultanas, pour evenly into the bundt tin.
Bake for 55-60 minutes or until an inserted cocktail stick comes out clean.
Use a small palette knife to carefully work around the the bundt tin to loosen the cake, making sure to also loosen the middle of the cake too. Carefully turn the cake upside down onto a wire rack then make the caramel.
For the caramel, melt the butter in a medium sized saucepan then add the marmalade and sugar and bring to a low boil, whisking until everything has dissoved. Boil for a couple of minutes then remove from the heat and stir in the sour cream.
Pour over the warm bundt.
Leave the cake to cool, then serve.