Melt butter and dark chocolate in the microwave until it is fully melted. Preheat oven at 190°C.
Add in sugar and mix until incorporated.
After that, add in egg one at a time. Stir until they are fully combined.
Fold in cocoa powder and all purpose flour.
Lastly add in walnuts.
Put into 7'x7' square cake pan. Bake at 190°C for 40 minutes. Once baked, let it cool and put it in the chiller.
For milk chocolate cream, microwave both milk chocolate and whipping cream until fully melted.
Pour oven the baked brownie. Put it back into the chiller until the cream is set.
Remove brownie from cake pan and cut them into rectangular shape of 5cm x 9cm.
In a mixing bowl, whip up non dairy cream until medium peak.
Transfer cream into piping bag with any shape nozzle that you have.
Pipe on the brownie and decorate it.