Pre-heat oven to 180C. Grease and line a cake tin.
Add hot water and vanilla to cocoa, mix. Put aside to cool.
Sift flour, baking soda and sugar together. Make a well in the centre. Stir mayonnaise into cocoa mixture.
Pour cocoa mixture into well and stir with a slotted/holed spoon. Pour into a greased, lined cake tin and bake for 35-40 minutes.
Ice when cool.
Rich Chocolate Glaze: Add chocolate and cream together in a metal or glass bowl over a pot of hot water. Stir until melted. Cool slightly and pour over cake.
