Preheat the oven to 350f and spray mini bundt pans with non stick cake release spray.
Whisk together the flour, salt and baking powder and set aside.
In a stand mixer, beat the butter and sugar until light and fluffy then add the eggs one at a time.
Add in the sour cream and vanilla extract and continue beating until combined. Don’t worry if the mixture looks split at this stage as once you add the flour, it will come back together and create a smooth batter.
Scrape down the sides of the mixing bowl then slowly add in the flour continuing to mix on low speed until just combined. Do not over mix.
Tip batter into a piping bag, no nozzle required.
Pipe into the cake pans, then place onto a baking tray and into the oven to bake for around 25-30 minutes until the top is springy to tough and a toothpick inserted into the centre of each cake comes out clean.
Leave in the tins to cool for five minutes before tipping onto a wire rack to cool completely.
Whilst the cakes are cooking, make the caramel for the buttercream. In a wide bottomed pan, place the sugar and heat over a medium heat. Wait until you can see the sugar melting then stir using a spatula until the sugar liquid has turned a light golden colour.
At this stage add in the butter carefully (it will bubble vigorously) and stir until it has melted and is fully mixed into the caramel.
Remove from the heat and pour in the double cream continuing to stir – again it will bubble so take care when doing this.
Pour into a jug and set aside to cool.