Combine the NESTLÉ Fat Free Sweetened Condensed Milk, melted butter, water and vanilla essence in a large bowl. Sift together the flour, cocoa, baking powder and baking soda. Stir the dry ingredients into the condensed milk mixture until just combined.
Pour the mixture into a lined 23cm spring form cake tin. Bake in a preheated 150°C oven for 45 minutes or until a cake skewer inserted into the centre of the cake comes out clean. Cool on a wire rack. For 10 minutes then remove from tin and cool completely. Ice top when cold
To prepare the icing, place butter in bowl. Add the sifted cocoa and icing sugar and sufficient boiling water to mix to a smooth but firm consistency.