Preheat your oven to 350°F and line an 8x8 or 9x9 inch baking pan with parchment paper. While the oven heats, prepare the espresso dipping liquid by combining 2/3 cup boiling water, 1.5 tablespoons espresso powder, and 1 tablespoon sugar in a small bowl, stirring until the espresso and sugar dissolve completely. Set aside to cool to room temperature—this needs to be cool before dipping the ladyfingers or they'll fall apart.

Melt 1/2 cup butter in a pot over medium heat, then add 7 oz semi-sweet chocolate and 1 tablespoon espresso powder, stirring constantly until completely smooth and combined. Remove from heat and stir in 1 1/4 cups sugar until fully incorporated. In a separate bowl, whisk together 3 eggs, 1 teaspoon vanilla extract, and 3 tablespoons vegetable oil, then add this mixture to the chocolate along with 2/3 cup cocoa powder and 1/4 teaspoon salt, stirring until no streaks remain. Finally, fold in 1/2 cup flour with just a few strokes—don't overmix, as this keeps the brownies fudgy rather than cakey.

Pour the brownie batter from Step 2 into your prepared pan and smooth the top with a spatula. Bake at 350°F for 27-32 minutes—they should be set on the edges but still slightly jiggly in the center, which means they'll stay moist and fudgy. Remove from the oven and let cool completely to room temperature before assembling the tiramisu layers.

While the brownies cool, beat 9 oz cold mascarpone cheese with 1/2 cup powdered sugar and 1.5 teaspoons vanilla extract on medium speed until smooth and creamy—don't overmix or the mascarpone can become grainy. I like to use cold mascarpone straight from the fridge because it holds its texture better during whipping. Slowly add 1 1/4 cups heavy cream while mixing, then increase speed to high and whip for 1-2 minutes until stiff peaks form. This creates that luxurious tiramisu texture that's both creamy and light.

Once the brownies from Step 3 are cooled, quickly dip each of the 12 ladyfingers into the cooled espresso mixture from Step 1 for just 1 second per side—a quick dunk is key to keep them from becoming soggy or falling apart. Arrange the dipped ladyfingers in a single layer on top of the brownies, then spread the mascarpone cream from Step 4 evenly over them in a thick, generous layer.

Refrigerate the assembled tiramisu brownies for at least 1 hour so the flavors meld and the cream sets up nicely. Just before serving, dust the top generously with 1 tablespoon cocoa powder using a fine sieve or sifter for an even coating. Slice into squares and serve chilled.