Place the frozen beetroot into a microwave container with ½ cup of water and cook on high for 8 minutes. Drain and allow to cool.
Heat the chocolate in a bowl of a double boiler and then allow to cool.
Preheat the oven to 180C / 350F
Process the beetroot in a food processor with the sunflower oil until a smooth consistency (there might still be a few very small chunks), about 3 – 4 minutes.
Separate the eggs and using an electric mixer, whip the whites until stiff peaks. Remove from the bowl and set aside.
In the same mixing bowl, add the egg yolks, sugars, beetroot and oil mixture, vanilla, salt, chocolate and almond flour and mix until well combined for about a minute.
Sift the flour, cocoa powder and baking powder and add them to the wet batter and briefly mix until incorporated.
By hand, gently fold through the whisked egg whites.
Line a 23cm x 13 x 8cm loaf tin (approx 1.5litre capacity) with baking paper. You could also make a layered cake and divide the batter between 2 lined 18cm cake tins (adjust the baking time down accordingly) or one bundt cake (just grease this vs lining with paper).
Decant the batter into the loaf tin and bake for 1 hour and 10 – 20 minutes and until a sharp knife comes out clean when inserted into the cake. Loosely cover with tin foil to prevent over-browning if necessary. * note that if you make this in a bundt tin or in 2 layers the baking time will need to be adjusted to around 1 hour.
Allow to cool in the tin for 10 minutes before removing to cool completely
Make the icing sugar by melting the chocolate in a double boiler and then allowing it to cool to room temperature.
Whip all the other ingredients together for a few minutes until fluffy. Ice the cake and then decorate the cake with chocolate shavings or walnuts.