Grease two 23cm / 9in non-stick springform cake pans with dairy-free butter. Line bottoms of the cake pans with greaseproof paper.
In a large bowl, sieve together the plain flour, caster sugar, 85g cocoa, baking powder and bicarbonate of soda.
Add the almond milk, vanilla extract and vegetable oil. Mix well.
Add the grated courgettes and mix until all is well combined.
Divide the mixture evenly between the two cake tins.
Cook for 25-30 mins until an inserted cake skewer comes out clean. Leave the cakes to cool for 5 mins in their tins then carefully remove sides of the spring form cake pans. Run a palette or rounded knife on the inside edge of the cake pans first to make sure the cake comes out neatly. Cool completely.
Once you are ready to ice the cake, prepare the chocolate icing. In a bowl, melt 75g of dairy free butter with the boiling water. In a separate bowl, mix together the icing sugar with 1 1/2 tbsp sieved cocoa powder. Add the melted butter to the sugar mixture. Blend well until you have a smooth icing.
Assemble the cake by placing one cake on a serving plate (having carefully removed the baking sheet). Spread some chocolate icing over the first cake then top with the other cake (from which you will also have carefully removed the baking sheet). Ice the cake all over with the chocolate icing with a palette knife. So it does not get too messy you can place some long strips of baking sheet around the edges of the cake while you ice it. Leave to icing to set (around 20 mins).