Preheat the oven to 180 C / Gas 4. Grease two 26cm cake tins and line with baking parchment.
Beat the butter and sugar together until pale and fluffy. Add the eggs, one at a time until creamy, followed by the vanilla extract and mix well. Add the flour, cocoa powder and baking powder a bit at a time, mixing until fully incorporated.
Measure out the buttermilk in a jug and add the red food colouring, stir together until red. Add to the cake mix and stir until the mixture turns red. Divide the cake mixture evenly between the two prepared cake tins.
Bake in the preheated oven for 25 to 30 minutes, or until a skewer inserted into the centre of the sponge comes out clean. Remove from oven and leave to cool for 10 to 15 minutes in the tin before turning out to cool on a wire rack to cool completely, about 1 hour.
For the buttercream:
Add the butter, cream cheese and vanilla extract to a bowl and mix together until smooth. Gradually add the icing sugar and mix until you have a creamy icing. Chill in the fridge for 30 minutes.
Place the first cake onto a serving plate then spread half of the buttercream on top. Place the second cake on top then spread the remaining buttercream over the top. Decorate with almonds, if desired. Slice and serve.
Experiment with red food colouring gels in addition to liquid as sometimes they can yield a brighter red result.