*how much red food colouring you use is completely dependent on the brand. Be careful using a very liquid food colouring (like Dr Oetker which is the default red food colouring you can get at most UK supermarkets) as it will affect the consistency of the batter. I love to use Squires Kitchen Professional Food Colour Pastes in my baking as they give excellent deep rich colours and don’t affect the recipe at all.
[recipe]*If you don’t have any buttercream to hand then you can make your own if you whisk together 400ml whole milk with 2 tablespoon white vinegar and let stand for 10 minutes before using. To this you can then add the 1½ tablespoons of white vinegar that the recipe requires.