Preheat your oven to 350°F (175°C) and line an 8x8-inch baking pan with parchment paper. In a medium bowl, whisk together gluten-free flour, cocoa powder, and a pinch of salt.

In a large mixing bowl, beat softened butter and sugar until creamy and fluffy, about 3 minutes. Add the eggs, one at a time, mixing well after each addition, followed by the vanilla extract.

Gradually add the dry mixture to the wet ingredients, folding gently until just combined. Pour the brownie batter into the prepared pan, smoothing the top with a spatula.

Bake for 25-30 minutes, until the edges look set and a toothpick inserted in the center comes out mostly clean. Allow the brownies to cool completely in the pan.

In a mixing bowl, combine mascarpone cheese, heavy cream, and espresso powder. Using an electric mixer, whip until smooth and thick, about 3-5 minutes.

Once the brownies are cooled, spread the tiramisu mixture over the brownie base using a spatula. Cover the pan with plastic wrap and refrigerate for at least 2 hours.

Dust the top lightly with cocoa powder before serving. Use a sharp, hot knife to cut into squares and serve chilled.