01 -
Line your baking pan (8 by 8 inches or 20 by 20 cm) with parchment and set your oven to preheat at 350°F (175°C). Start off by mixing up the melted butter, sugar, eggs, and vanilla in a bowl till they're blended. Toss in the cocoa, flour, baking powder, and salt. Carefully fold these dry bits into the wet stuff until it comes together—don’t beat the heck out of it or you’ll get tough brownies. Pour everything into your pan and smooth it out.
02 -
Pop the pan into your hot oven, bake for about 20 to 25 minutes. When a toothpick poked in the middle comes out with a few sticky crumbs, pull it out and let it sit in the pan until it's totally cool.
03 -
Warm up the milk in a little pot—don't let it boil, just get it nice and hot. Dump the chopped chocolate into a heatproof bowl and pour the steamy milk over it. Hang tight for a couple of minutes, then stir it until it turns totally smooth and glossy. Let the chocolate cool down to room temp, keeping it nice and runny. In another bowl, whip the cold heavy cream with powdered sugar until it gets soft peaks. Gently mix the cooled chocolate blend into the cream just until they come together. Spread this mousse over your fully cooled brownies. Chill in the fridge for at least two hours so it can set.
04 -
Toss the chopped chocolate in a bowl. Warm up the heavy cream on the stove until it starts to simmer, then pour it over the chocolate pieces. Wait two or three minutes. Stir the mix until the ganache turns silky and shiny. Pour that over your set mousse and use an offset spatula to smooth it out. Stick the whole thing back in the fridge for at least an hour so the top firms up.
05 -
After the ganache is set nice and firm, grab the edges of the parchment to lift the brownie block from the pan. Slice into 12 squares using a sharp knife. For the best layers, clean your knife after each cut so things look neat.