In a medium saucepan, combine 140g of granulated sugar and 1½ tablespoons of water over medium heat. Stir gently until the sugar dissolves, then increase the heat without stirring until the mixture turns a golden brown, about 7-10 minutes. Remove from heat and carefully whisk in 40g of butter and 150g of heavy cream, followed by a pinch of salt. Allow the caramel to cool fully before chilling it in the fridge.

Preheat your oven to 170ºC (340ºF) and grease three 20 cm round cake pans. In a large mixing bowl, sift together 340g of all-purpose flour, 2 tablespoons of cornstarch, ¾ teaspoon each of baking powder, baking soda, and ¾ teaspoon of salt. In another bowl, cream 180g of softened butter with 200g of granulated sugar until light and fluffy, about 4-5 minutes. Gradually add 4 large eggs, mixing one at a time, then blend in 240g of sour cream, 60g of vegetable oil, and 2 teaspoons of vanilla extract.

Gently fold half of the dry ingredients into the wet mixture until just combined. Then, add the remaining dry mix and mix until smooth. Divide the batter equally among the prepared pans and smooth the tops. Bake for 20-23 minutes or until a toothpick inserted in the center comes out clean. Remove the cakes from the oven and cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

While the cake cools, make the buttercream. In a large bowl, beat 400g of softened butter with an electric mixer for about 4 minutes until creamy. Gradually add 660g of powdered sugar, mixing until incorporated. Then, drizzle in your cooled salted caramel while continuing to beat until the buttercream is fluffy and light in texture.

Once the cake layers are completely cool, place the first layer on a serving plate. Spread a generous layer of buttercream over the top, followed by a drizzle of salted caramel. Add the second layer of cake and repeat the process. After placing the final layer on top, apply a thin crumb coat of buttercream around the sides and top. Chill in the fridge for 20 minutes to set.

After chilling, spread a thicker layer of the remaining buttercream over the top and sides for a smooth finish. Drizzle extra salted caramel over the top as a beautiful garnish and, if desired, sprinkle some sea salt for an extra touch. Your Salted Caramel Cake is now ready for slicing!