Preheat oven to 350º F.
In measuring cup mix ground flax seed and water and let stand for 5 mins.
In a bowl add cocoa powder, boiling water, flax egg, sugar, vanilla and combine well.
In another bowl combine flour, baking powder and soda.
Gradually add flour mixture to wet mixture and mix well.
Pour into greased baking pans and bake for 35 minutes or until a toothpick inserted comes clean.
Cool in pans for 10 minutes and then transfer to a rack until completely cooled.
In a mixer with paddle attachment, cream butter.
Add vanilla and cocoa powder and mix well.
Gradually add icing sugar and mix until fluffy.
You may add 1-2 tbsp of plant milk to soften if icing is too stiff.