Preheat the oven to 325F, and line an 8x8 baking dish with parchment.

In a microwave-safe bowl, heat the butter and chocolate chips in 15 second intervals until smooth and melted.

Stir in the sugar and cocoa powder, followed by the mascarpone cheese, eggs, vanilla, and espresso powder. Finally, add in the flour and salt.

Pour the batter into the prepared pan, and bake for 40-50 minutes, until a toothpick inserted in the center comes out mostly clean. Bake slightly less for more fudgy brownies and more for cakey brownies. Serve with additional mascarpone cheese spread on top!