Around half an hour before you are ready to top the brownie with the ganache, break up the chocolate and add it to a bowl.
Heat the whipping cream in a pan until it just starts to boil. Remove from the heat and pour over the broken chocolate.
Stir until the chocolate has fully melted.
Put the ganache in the fridge for 10 mins, remove and whisk on high speed for 2-3 mins. Repeat until the ganache has thickened enough to spread and hold its shape. It should be lighter in colour and fluffy.
Remove the brownie from the tin.
Spread approx. half of the ganache over the brownie and add the other half to a piping bag with your chosen nozzle attachment.
Pipe the ganache around the edge of the brownie, add any other decorations you wish and you are ready to serve.