340gunsalted butter, cool but slightly softened (3 sticks / 1 ½ cups)
FOR THE BLACK VELVET CAKE
Preheat the oven to 180C / 350F / 160C fan forced.
Grease 3 round 8 inch sandwich tins (cake pans). Dust all over with cocoa, tapping out the excess.
In a very large bowl, sift the flour, black cocoa, baking soda and baking powder together. Add the sugar and salt and use a balloon whisk to gently whisk it all together.
In a medium bowl, add the butter, oil and buttermilk. Whisk to combine.
Add the eggs, vanilla and vinegar, then whisk those in too - just until combined.
Make a well in the centre of the flour mixture and pour in the wet ingredients. Use a spatula to gently fold and stir together just until smooth. Be careful to dig right to the bottom of the bowl to make sure all the flour is combined.
Evenly divide the batter between the three tins (you can weigh it to be extra sure but eyeballing is fine). Level out on top.
Bake for 22-24 minutes, turning the trays at about the 15 minute mark, until a toothpick comes out just clean.
Rub vinegar around the inside of your mixing bowl, rinse out and dry.
Heat about 1 inch of water in a medium saucepan until simmering.
Add the egg whites to the mixing bowl, then the sugar. Whisk together with a balloon whisk until combined.
Place the bowl over the simmering water and continue to gently whisk and stir for around 5 minutes, until the temperature of the mixture reaches 71C / 160F. Rub a little of the mixture between your fingers to make sure there are no sugar granules left. If there are still granules, remove from heat and keep stirring until they're gone.
While still hot, place the bowl in your stand mixer and fit a whisk attachment. Whisk on medium-high speed to stiff peaks, making sure the bowl and meringue have cooled to at least room temperature. If not, you may set it aside until it does.
Swap to the paddle attachment, then add the butter about 1 tablespoon at a time and beat at medium-high, until it's mixed in before adding the next tablespoon. Continue like this until it's all combined.
It should be looking thick, smooth and creamy. Add the vanilla and salt and mix for a good 20 seconds to make sure it's all combined.
Transfer the buttercream to a piping bag, if using.
Place one of the cake layers onto a cake plate and pipe or spread 1/3 of the frosting over it. Repeat with the second and third layers, only placing them on top of the previous layer once piped - this will stop your buttercream from squishing out the sides.
Make sure to use a very sharp knife for cutting. Being a 3 tiered cake, you may find it easier to chill the cake so that it's firm before cutting too.
For best results you should always weigh ingredients like flour and sugar. Kitchen scales are relatively cheap but if you can’t weigh the ingredients, use the spoon and level method (don’t scoop).
All ovens vary - check for doneness 2-3 minutes before the recipe suggests.