Grease the slow cooker bowl (would recommend if using butter to put on wax paper or baking/parchment paper to do).
In a separate bowl, combine the first 7 ingredients mixing or whisking well together.
Sift brown sugar and extra cocoa powder over mixture.
Using a spoon, gently and evenly pour the boiling water over the mixture.
Cook on HIGH for 2 1/2 hours, or until centre is firm (I think cooking time could vary depending on the size of your crock pot/slow cooker - mine is a 6L oval shaped cooker and this is the time they recommend).
Serve with sifted icing sugar and ice cream or cream.