Preheat your oven to 350°F and line a 9x9-inch pan with parchment paper.
In a large bowl, whisk together melted butter, granulated sugar, and brown sugar until smooth.
Add eggs and vanilla extract, mixing until fully combined.
Sift in flour, cocoa powder, and salt. Fold gently until just combined.
Pour the brownie batter into the prepared pan and bake for 30 to 35 minutes, until a toothpick comes out with a few moist crumbs.
Let the brownies cool completely, then evenly brush the surface with the cooled coffee.
In a separate bowl, beat mascarpone cheese until smooth.
In another bowl, whip the heavy cream, powdered sugar, and vanilla until stiff peaks form.
Gently fold the whipped cream into the mascarpone mixture.
Spread the mascarpone topping evenly over the cooled brownies.
Refrigerate for at least 2 hours to set.
Just before serving, dust the top with cocoa powder.