Preheat the oven to 175 C / 350 F (no fan) and prepare a 9-inch / 23 cm brownie tin. Brush the inside of the pan with a tiny bit of oil, and then line the bottom and sides with parchment paper.
Gently melt the butter and the chocolate in a bowl over simmering water over low-medium heat. Alternatively, use your microwave; however, ensure that you don't burn the chocolate.
In another bowl, whip together the eggs with sugar with the help of an electric hand mixer or stand mixer until pale, for about 5-7 minutes.
Slowly pour the melted butter and chocolate mixture into the egg-sugar mixture while the mixer is on low speed.
Lastly, sift the dry ingredients (flour, salt, and cocoa powder) into the wet ingredients, and fold the mixture together with a rubber spatula. Do not overmix.
Pour brownie batter into the prepared baking pan and smooth the top with an offset spatula.
Bake the brownie at 175 C / 350 F for about 35 minutes. The brownie is ready when the edge looks baked and the middle looks slightly gooey but not raw. Do not over-bake! The brownie will set further as it cools.
Let the brownie completely cool in the pan before proceeding with the tiramisu part.
Make the tiramisu layer
Place the cold mascarpone in a mixing bowl. Add very cold heavy cream to the bowl along with sifted powdered sugar. Whip the mixture with an electric hand mixer. After 3-4 minutes, when the mascarpone cream reaches a fluffy, pipeable consistency. Stop right there, do not overwhip the mascarpone cream, as it can break.
Divide the mascarpone cream into two equal portions. Spread one half on top of the brownies.
Soak the ladyfingers in the coffee, and then place them next to each other on top of the mascarpone cream. Finally, spread the other half of the mascarpone cream on top and then smooth the top with an offset spatula.
Refrigerate the tiramisu brownies for a minimum of one hour to set and the ladyfingers to soften.
Dust with cocoa powder before serving. Any leftovers can be stored in an airtight container refrigerated for 2-3 days.
Notes
INGREDIENT NOTES
Use unsalted butter to make the brownies and add the salt separately. This way, you are in control of the quantity of the salt.
The egg should be used at room temperature when making the brownie.
Baking powder is intentionally omitted from the recipe, so your brownies turn out wonderfully fudge and gooey.
The quality of the chocolate chips and the cocoa powder will define the taste of your brownies, so try to use high-quality ingredients, e.g., semi-sweet chocolate from Lindt or Callebaut and Dutch-processed cocoa powder.
For the mascarpone frosting, refrain from using low-fat products as they won't whip up light and fluffy.
TECHNIQUE NOTES
A digital scale is required for a consistent, happy baking experience.
If your preferred chocolate melting method is a microwave, not the double boiler, use a plastic container to melt it. The glass can very quickly heat up and might burn your chocolate.
Always preheat your oven and consider using a digital oven thermometer for the best results.
Each oven is different, so you might need to adjust the baking time +/- 5- 10 minutes.
For the best fudge brownie experience, consider slightly underbaking your dessert.