Preheat your oven to 350°F (175°C) and grease an 8x8 or 9x9 baking pan. In a large mixing bowl, melt the butter, then stir in granulated and brown sugars until well combined. Add the eggs one at a time, mixing until smooth. Gradually blend in the gluten-free flour and cocoa powder, ensuring no lumps remain. Pour the mixture into the prepared pan and spread it evenly. Bake for 25 minutes, then let the brownies cool completely in the pan.

While the brownies cool, prepare the tiramisu topping. In a separate mixing bowl, combine mascarpone cheese, espresso powder, and heavy cream. Using a hand mixer or stand mixer, whip the mixture on medium speed until it becomes fluffy and holds stiff peaks, about 3-5 minutes.

Once your brownies are cooled, carefully spread the light and fluffy tiramisu topping over the cooled brownie base using a spatula for an even layer.

Transfer the pan to the refrigerator. Allow the Tiramisu Brownies to chill for at least 2 hours.

Dust the top generously with cocoa powder just before serving and slice into squares with a hot knife for clean cuts.