Prepare the oven and pan

• Preheat the oven to 180 °C.
• Line a baking dish with parchment paper.

Melt the butter and chocolate

• Melt the butter with the chopped bittersweet chocolate in a saucepan over low heat.
• Whisk until smooth, then set aside to cool slightly.

Make the brownie batter

• Whisk the eggs with the dark brown sugar and granulated sugar until pale and glossy.
• Stir in the vanilla extract, instant espresso powder and salt.
• Fold in the melted chocolate mixture, then the dutch cocoa powder and flour until just combined.

Bake the brownies

• Pour the batter into the prepared dish and spread evenly.
• Bake until the center is just set and a toothpick comes out with moist crumbs.

Whip the espresso cream

• Beat the mascarpone with the granulated sugar, salt, vanilla bean and instant espresso powder.
• Pour in the cold heavy cream and whip until thick and spreadable.

Assemble and chill

• Spread the espresso cream over the cooled brownies.
• Chill until the cream is firm.

Dust and serve

• Dust the top with unsweetened cocoa powder through a sieve.
• Cut into squares and serve.