01 -
Preheat oven to 175°C (350°F). Line an 8×8-inch (20×20 cm) baking pan with parchment paper. In a mixing bowl, whisk together the melted butter, granulated sugar, eggs, and vanilla until smooth. Sift in the cocoa powder, flour, salt, and baking powder, then gently fold into the wet ingredients until just combined. Avoid overmixing. Pour batter into prepared pan, smooth with a spatula, and bake for 20-25 minutes. A toothpick inserted should come out with a few moist crumbs. Cool completely in the pan.
02 -
Heat the milk in a small saucepan until steaming (not boiling). Pour over the chopped semisweet chocolate in a heatproof bowl. Let sit for 2 minutes and stir until smooth. Let cool to room temperature. In a separate bowl, whip the heavy cream with powdered sugar until soft peaks form. Gently fold the cooled chocolate mixture into the whipped cream until fully incorporated without deflating the mousse. Spread evenly over the cooled brownie base and refrigerate for at least 2 hours until set.
03 -
Place the chopped chocolate in a heatproof bowl. Heat heavy cream in a small saucepan until it starts to simmer. Pour over chocolate and let sit for 2-3 minutes. Stir until smooth and glossy. Pour over mousse layer, spreading evenly with an offset spatula. Refrigerate for 1 hour until firm.