Preheat the oven to 180°C (gas mark 4/350°F). Line a muffin tin with 12 muffin cases.
Weigh out the butter, sugars, eggs and vanilla into a mixing bowl. Sift the flour over the top, then whisk the ingredients together with an electric whisk until the mixture is completely blended and creamy (you could also whisk by hand, but be sure to soften the butter first if you do).
Divide the mixture equally between the 10 cupcake cases and smooth the tops. Pop into the preheated oven and bake for 16-18 minutes until risen and golden.
Once the cakes are cool enough to handle (but still warm), fill each cake with the salted caramel cupcake centre mixture, following packet instructions. Transfer the cupcakes to a wire rack to cool.
Once completely cool, make the icing. Soften the butter slightly (weigh it out and pop it into the microwave for 10 seconds if using straight from the fridge), then whisk with an electric whisk until creamy.
Sift half of the icing sugar into the bowl with the butter and whisk until combined (this may take a little while, so do persevere with it!). Add the carnation caramel and sift in the rest of the icing sugar, then whisk until combined and smooth.
Spoon the icing into a piping bag fitted with a large closed star nozzle. Pipe a generous swirl on top of each cake and top with gold sprinkles if wanted.