Instructions

1. Preheat the oven to 180°C/350°F/gas 4 then lightly grease 3 (20cm/8inch) round cake tins. Line the bottom of each tin with a round of parchment paper.
2. To make the sponge, combine the butter, sugar and salt in a large bowl and beat with an electric mixer until pale and creamy. Add the vanilla, then slowly add the egg whites while beating until all of the egg whites have been whisked in completely.
3. Sift together the flour and baking powder. Add one third of the dry ingredients to the butter mixture and beat just until combined. Add half of the buttermilk and again mix only until combined. Mix in half of the remaining dry ingredients, followed by the last of the buttermilk. Then finally fold in the remaining flour until just combined.
4. Divide the batter evenly between the prepared cake tins and gently smooth the top with a spatula, then bake sponges for 25-30 minutes until a toothpick inserted in the middle comes out clean and the top of the sponge bounces back when lightly pressed.
5. Remove from the oven and leave to cool for about 10-15 minutes, then carefully turn cakes out of tin onto wire racks. Peel away the parchment paper and leave to cool completely.
6. To make the buttercream, in a large bowl, beat butter with an electric mixer until smooth. Sift in icing sugar and add milk or cream, vanilla (or other flavourings) and salt. Start beating together with mixer on lowest speed, once icing sugar has been mixed in, increase speed and beat until frosting is smooth and creamy. Make sure to scrape down the sides of the bowl so that everything is well incorporated.
7. When ready to assemble and decorate, place one of the sponges on a cake plate or serving dish. Spread about ½ cup buttercream over the top of the sponge, then gently place a second sponge on top, gently pressing down to make sure it’s sitting properly and that it’s level. Spread another ½ cup buttercream over the top of the sponge and place the final sponge on top.
8. Coat the entire cake with a crumb coating of buttercream, which is just a very thin layer of buttercream used to trap any loose crumbs. Place cake in the fridge and allow crumb coat to firm, about 15-20 minutes. Cover the bowl with the remaining buttercream with clingfilm. Once crumb coat is set, remove from the fridge. Give the remaining buttercream a quick mix with a spatula, then finish icing the cake with a thick layer of the frosting. Use a large flat spatula to get lovely smooth sides and top, or leave it more rustic with lovely swirls of frosting.
9. To finish off, fill a piping bag fitted with a star tip with any remaining buttercream and pipe a border around the bottom of the cake. Finally, decorate with coloured sprinkles or sugars.
10. Sponges can be made up to a day before decorating and each sponge kept in an airtight freezer bag at room temperature. Buttercream can be made up to 3 days ahead and kept in the fridge. Leave at room temperature for about 1-2 hours, then beat on low speed until it’s lovely and creamy again.
11. Store cake at room temperature in an airtight cake tin. Will last 2-3 days.