Preheat the oven to 180ºC and line the bottom and sides of an 8-inch square pan (2-3 inches thick) with parchment/baking paper. Set the square pan aside.

Melt the chocolate and butter in a metal bowl over a saucepan of simmering water (double-boil) until it is well incorporated. Remove from heat and whisk in sugar and cocoa powder.

Next, add in vanilla extract and eggs (one at a time). Beat the mixture well using a whisk or spatula after each addition.

Then, stir in the flour and walnuts. Pour mixture into prepared pan and bake it for 25-30 minutes or until toothpick inserted in the center comes out with a few moist clumps clinging on it. Do not over bake! When it's ready, take out from the oven and cool.

While waiting for the brownie to cook or cool, finely chop or grate the chocolate and put them into a heatproof bowl. Next, heat the heavy cream on medium heat until it starts to boil. Immediately pour the boiling cream over the chopped chocolate and let it sit for 1 minute before stirring.

After 1 minute, stir the chocolate with a spoon or spatula until all is melted and mixed well. Pour the ganache on the brownie and let it set on the counter for 10 minutes.

Finally, it's time to eat! Enjoy your gooey-moist-decadent brownies! :D