This salted caramel sponge is layered with salted caramel frosting for complete decadence. Equipment and preparation: You will need 3 x 18cm/7in cake tins.
For the cake
250g/9oz unsalted butter, softened, plus extra for greasing
100g/3½oz golden caster sugar
100g/3½oz soft light brown sugar
100g/3½oz golden syrup
4 medium free-range eggs, lightly beaten
2 tsp vanilla bean paste
350g/12oz self-raising flour
1 tsp baking powder
½ tsp sea salt flakes, crushed
100ml/3½fl oz milk
For the salted caramel
250g/9oz caster sugar
125g/4½oz soured cream
30g/1oz unsalted butter
1 tsp vanilla bean paste
½ tsp sea salt flakes
For the frosting
250g/9oz unsalted butter, softened
2 tsp vanilla bean paste
425–450g/15oz–1lb icing sugar, sifted
3–4 tbsp milk
Heat the oven to 180C/160C Fan/Gas 4. Grease and line the bases of 3 x 18cm/7in cake tins with buttered baking paper.
To make the cake, cream the butter with the golden caster sugar, soft light brown sugar, and golden syrup for about 5 minutes in a free-standing mixer fitted with a creamer attachment (or using hand-held beaters) until the mixture is pale and light. Add the eggs one at a time, beating well between each addition and scraping down the sides of the bowl with a rubber spatula. Add the vanilla and mix again to combine. Sift the flour, baking powder, and salt into the bowl and fold in until almost combined. Fold in the milk until nearly smooth, then mix for 30 seconds in the stand mixer until silky smooth.
Divide the mixture evenly between the prepared tins and spread level with the back of a spoon or a palette. Bake on the middle shelf of the preheated oven for 25 minutes, or until well risen and a wooden skewer inserted into the middle of the cake comes out clean. Leave the cakes to cool in the tins for 2–3 minutes and then turn out onto a wire rack and leave until cold while you make the salted caramel sauce.
To make the salted caramel, tip the caster sugar into a medium-sized, heavy-bottomed saucepan and add 2 tablespoons of water. Set the pan over low heat to dissolve the sugar without stirring, but gently swirl the pan from time to time. Brush the sides of the pan with water to melt any sugar crystals that may have formed and stuck to the inside of the pan. Once all of the sugar has dissolved increase the heat to medium and bring the syrup to a boil. Continue to cook until the syrup becomes a deep amber color, swirling the pan to ensure that the caramel cooks evenly.
Carefully slide the pan off the heat and add the soured cream and butter and stir gently to combine. Return the pan to low heat to re-melt any hardened caramel. Add the vanilla and salt, mix to combine, and pour the caramel into a bowl. Cool until needed.
To make the frosting, cream the butter with 150g/5½oz salted caramel and the vanilla in a free-standing mixer fitted with a paddle attachment for 3–4 minutes, or until soft and light. Gradually add the sifted icing sugar and milk, and beat until thoroughly combined. Scrape down the sides of the bowl with a rubber spatula and continue to beat for a further 3–4 minutes, or until the frosting is light and fluffy.
To assemble the cake, place one cake layer on a cake serving plate and spread the top with 1 tablespoon of the salted caramel and then 3 tablespoons of the buttercream frosting. Top with another cake layer and repeat spreading with the salted caramel and buttercream and ending with the third cake layer. Cover the top and sides of the cake with a thin coat of buttercream and chill in the fridge for 30 minutes until firm. Set the remaining frosting aside at room temperature.
Cover the top and sides of the cake with another smooth layer of buttercream and pipe any leftover frosting over the top of the cake. Drizzle the remaining salted caramel over the top and down the sides of the cake and serve.