Preheat the oven to 350°F (175°C). Grease and flour a 9×9-inch metal baking pan, or line it with parchment paper.

In a medium bowl, whisk together the flour, cocoa powder, and salt. Set aside.

Melt the chopped chocolate and butter together in a double boiler, stirring until smooth and completely combined.

Add the granulated sugar and brown sugar to the melted chocolate mixture. Whisk until well combined.

Remove the chocolate mixture from the heat and allow it to cool to room temperature.

Once cooled, whisk in the eggs one at a time until fully incorporated. Stir in the vanilla extract.

Add the flour mixture and whisk just until no dry streaks remain. Avoid overmixing.

Pour the brownie batter into the prepared pan and spread it evenly.

Bake for 20–30 minutes, or until a toothpick inserted into the center comes out with a few moist, fudgy crumbs.

Let the brownies cool completely in the pan at room temperature.

For the topping, combine the heavy cream and espresso powder in the bowl of a stand mixer or large mixing bowl. Mix until the espresso powder has dissolved.

Add the mascarpone cheese, powdered sugar, and vanilla extract. Beat on medium speed until the mixture becomes light and fluffy.

Spread the mascarpone cream evenly over the cooled brownies.

Sift the cocoa powder over the mascarpone layer to create a delicate cocoa finish.

Refrigerate the tiramisu brownies for at least 1 hour, or until the mascarpone layer is firm and set.

Slice into squares and serve chilled.