In a bowl combine cocoa powder, sugar and self raising flour and stir to blend.
In a separate bowl beat together egg and melted butter until well combined. Add the dry ingredients and stir until the mixture becomes smooth.
Transfer the batter into a greased pan (use a very small pan as this is half the yield of a normal brownie). Bake for about 20 minutes or until a toothpick inserted in the centre comes out clean.
Let cool until room temperature and then cut into bite sized pieces.
Using an electric mixer beat together cream cheese, vanilla and powdered sugar until creamy.
In a large mixing bowl whip the cream until very thick. Let sit in the fridge until preparing the rest of the ingredients.
In a heatproof bowl combine ground pistachio, milk and white chocolate. Place the bowl over a pan of gently simmering water. Stir from time to time until the chocolate is melted and the three ingredients are combined into a thick mixture.
With a rubber spatula gently fold the chocolate mixture into the cream cheese. Fold in also the whipped cream, mixing very carefully until uniform.
Arrange half of the brownie bites on the bottom of 4 to 6 glasses (depending on their size). Spoon the pistachio mousse over the brownies. Arrange the rest of the brownie bites on top.
Cover with cling film and let sit in the fridge for 2-4 hours before serving.