Step 1: Prepare Your Baking Pan

Preheat your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving an overhang on all sides for easy removal later.

Step 2: Make the Brownie Batter

1. In a medium microwave-safe bowl, combine the butter and chocolate chips. Microwave in 30-second intervals, stirring between each, until completely melted and smooth.
2. Stir in the brewed coffee while the chocolate mixture is still warm.
3. Allow the mixture to cool slightly, then whisk in both sugars until well combined.
4. Add the eggs one at a time, whisking well after each addition.
5. Stir in the vanilla extract.
6. In a separate bowl, whisk together the flour, cocoa powder, salt, and baking powder.
7. Gradually fold the dry ingredients into the wet ingredients until just combined. Do not overmix.

Step 3: Bake the Brownies

1. Pour the brownie batter into the prepared pan, spreading it evenly.
2. Bake for 20-22 minutes until the center is just set and a toothpick inserted comes out with a few moist crumbs.
3. Remove from the oven and allow to cool completely in the pan.

Step 4: Prepare the Tiramisu Topping

1. In a medium bowl, beat the mascarpone cheese until smooth.
2. In a separate bowl, whip the heavy cream until soft peaks form.
3. Add the powdered sugar, vanilla, coffee liqueur (if using), and cooled coffee to the mascarpone and mix until combined.
4. Gently fold the whipped cream into the mascarpone mixture until smooth and well incorporated.

Step 5: Assemble the Tiramisu Brownies

1. Once the brownies are completely cool, spread the tiramisu topping evenly over the brownie layer.
2. Dust the top generously with cocoa powder, using a fine-mesh sieve.
3. If desired, add chocolate shavings for extra decoration.
4. Refrigerate for at least 2 hours, or ideally overnight, to allow the flavors to meld.

Step 6: Serve and Enjoy

1. Remove the brownies from the refrigerator 15-20 minutes before serving.
2. Use the parchment paper overhang to lift the entire dessert out of the pan.
3. Cut into squares with a sharp knife, wiping the blade clean between cuts for neat edges.