Put cocoa into a medium saucepan and slowly whisk in the hot water to form a smooth paste. Add sugar, butter and chocolate. Stir over low heat until melted and smooth. Remove from heat and set aside for 15 minutes to cool. Stir in the almond meal and eggs. Pour into tin and bake for about 60-70 minutes for the two deep 22cm cakes, 50 minutes for thinner 22cm (9 in) cake, and 1 hour 20 minutes for 16cm (6 in) cake or until cooked when tested with a skewer. I baked the 9 inch cake for 1 1/2 hours to get the toothpick to come out clean but read elsewhere that flourless cakes can be taken out when the middle is still a bit jiggly otherwise they can be a bit dry. Not sure if that applies to this cake. The cake wasn't overly dry but I will try a bit less time in the oven next time. Cool cake in the tin, then remove, cover and refrigerate until needed. They can all be frozen at his stage if you are planning ahead. Cool, wrap in baking paper then cling film and freeze flat (on a tray is good). Defrost over night .
Beat the egg whites with a electric hand mixer in a large bowl until firm peaks form. Continue beating and pour in the sugar syrup in a steady stream into the egg whites. Beat for 3 minutes or until the mixture stops steaming.
Continue beating and add the butter, a few cubes at a time, until it's all incorporated. Beat for a further 15 minutes (the mixture will look curdled at first), then use a metal spoon to mix in the vanilla. Keep in a cool place (not in the fridge) until needed.
To ice I turned the cake upside down on the serving plate as the bottom of the cake is flatter. For the 9 inch cake the above amount of icing was too much. I would try 2/3 of the recipe next time.
Garden flowers made a pleasing finish to the cake.