Beetroot Red Velvet Cake: New Year's Eve Dinner part 2

I was looking for a suitably special cake to go with the Seitan a l'Orange main course for a New Year's dinner, and I came up with this one.
I've done a bit of research and I've found that traditionally, the red colour of this cake was achieved by a chemical reaction between the vinegar used and the lighter, unrefined cocoa available in those days. I only have the regular cocoa (although it is organic) and can't use vinegar as it isn't offerable to Krishna and is nor in the Mode of Goodness. But what I do have is some homegrown organic beetroot just waiting to become the healthy ingredient in an otherwise nutritionally-lacking cake. If you visit here regularly, you may recognise this cake recipe as an adaptation of my Sweet Potato Muffins. This was the first time I'd ever made (or eaten) red velvet cake, and I'll definitely be doing it again, maybe next time as cupcakes with the piped icing and sprinkles. There's a kind of yummy synergy to beetroot and cocoa- my husband suggested it's because they are both iron-rich.  As you can see from the picture, however, it's really more of a reddish-brown velvet cake; I could use less cocoa next time and maybe also add a little natural red food colouring (beetroot concentrate) to the cake mixture.
400g self-raising flour
200g demerara sugar (use xylitol if you like)
2 tabs cocoa powder
4 tsps baking powder
150g grated fresh beetroot
400ml soya milk
150ml sunflower oil/ rice bran oil

• In a bowl, combine all the dry ingredients except the beetroot
• In another bowl, combine the oil and soya milk
• Mix the beetroot to the dry ingredients
• Add the wet ingredients and beat well for about a minute
• Put into dampened 8-10" silicone moulds/ greased and floured tins and bake in a preheated oven at 180C for 20-30 mins, until a skewer inserted into the centre of one of the cakes comes out clean. (The cake is very soft, so don't mistake that for it not being cooked through.)
• Fill and frost with vanilla buttercream (I used the best part of a packet of Pure sunflower unhydrogenated vegan margarine and lots of icing sugar- you could grind xylitol to a powder for this.) When I added the vanilla essence to the frosting, however, it caused the water to separate out and I had to put it in the freezer to solidify it; so I will definitely use vanilla sugar next time so that I can pipe it. Scatter with chocolate sprinkles, or red-coloured sugar granules.