In a large mixing bowl, whisk together gluten-free flour, unsweetened cocoa powder, granulated sugar, and espresso powder until well combined. Melt the butter and let it cool slightly, then mix it into the dry ingredients along with the eggs. Stir until the brownie batter is smooth and homogeneous, ensuring no dry spots remain.

Preheat your oven to 350°F (175°C). Grease an 8x8-inch baking pan and pour the brownie batter into it, spreading it evenly. Bake in the preheated oven for about 25 minutes or until a toothpick inserted in the center comes out with a few moist crumbs. Allow the brownie layer to cool completely in the pan on a wire rack.

While the brownies are cooling, take a medium mixing bowl and add mascarpone cheese, granulated sugar, and vanilla extract. Using an electric mixer, beat the mixture on medium speed until it becomes creamy and smooth, which should take about 2-3 minutes. Be careful not to over-mix.

Once the brownie base has completely cooled, spread the creamy tiramisu mixture evenly over the top. Cover the pan with plastic wrap or foil, and refrigerate the layered dessert for at least 2 hours.

Before slicing into your Gluten Free Tiramisu Brownies, dust the top generously with cocoa powder. Use a sharp knife dipped in hot water for clean cuts, and serve chilled.