Preheat the oven to 185°C.
Line the bottoms of a 6" cake tin, with parchment and butter the sides.
In a bowl, take the cocoa, brown sugar and pour in the boiling water. Whisk to mix, then set aside.
Cream the butter and powdered sugar together, beating well until pale and fluffy. Add vanilla essence and cream again.
Mix in the 2 tbsp egg replacer with 6 tbsp water and keep it aside.
In another bowl, sift the flour with baking powder, baking soda.
Now add the egg replacer and the flour alternatively to the cocoa mix, beat well.
The last flour batch can be gently folded into the batter.
Pat it down well and bake for 30 mins.
I baked further at 170 for 20 mins.