Turn on the oven to 175 Celsius or 350F
Mix the milk and cider vinegar and leave to stand
Sift the flours and mix them in a bowl with all other dry ingredients
Grind the flaxseeds and mix them with water.
Mix oil, agave syrup and lemon juice
Mix flax and oil mixture with a spoon and add into dry ingredients, then add milk and mix again. Do it gently, do not over mix it because if you do it too harsh the cake could turn out chewy. Fold in the grated apple. Alternatively you can use apple sauce (say, 1/2 cup)
The batter should be fairly thick but still pourable
Pour the ready batter into a lined cake tin (I used 24cm tin to get a higher cake, but 27cm is for a "normal"cake )
Bake for 35-40 minutes. Baking time will depend on the thickness of the batter. In a wider pan the batter will be thiner and will require shorter baking time.
Test the cake with the tooth pick. When it's done the tooth pick should come out clean
Prepare the frosting: drain and wash the cashews and place them in the blender.
Melt cocoa paste in a bowl over the pot with boiling water.
Add it to cashews and the rest of the ingredients besides cocoa powder.
Blend until smooth. It's best to use a professional blender to get a very smooth consistency without needing to water it down too much
Add cocoa powder and blend until nicely incorporated
Leave it in the fridge until it firms up
When the sponge is cooled down you can assemble the cake.
It will keep in the fridge for 7 days or longer.