Preheat your oven to 350°F (175°C) and prepare a 9x9-inch baking pan by lining it with parchment paper.

In a medium bowl, combine chopped dark or semi-sweet chocolate with natural cocoa powder. Heat unsalted butter in a small saucepan until browned, then pour it over the chocolate mixture.

In a separate bowl, whisk together eggs, granulated sugar, and brown sugar until the mixture is light and pale. Gradually add the melted chocolate mixture, and fold in all-purpose flour gently until just combined.

Spread the brownie batter evenly into the prepared baking pan. Bake in the preheated oven for 28-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs attached.

Remove the brownies from the oven and let them cool in the pan on a wire rack for about 30 minutes.

In a bowl, whip together mascarpone cheese, heavy whipping cream, powdered sugar, and vanilla extract until thick and creamy, about 3-5 minutes.

In a shallow bowl, dissolve espresso powder in hot water, adding coffee liqueur if desired. Quickly dip each ladyfinger for 1-2 seconds to soak.

Spread the whipped mascarpone cream evenly over the soaked ladyfingers, smoothing it out with a spatula.

Cover the assembled Tiramisu Brownies gently and refrigerate for at least 1 hour to allow the layers to meld and the cream to set.

Dust a light layer of cocoa powder on top before slicing.