Preheat the oven to 175℃ / 350℉. Line a 23cmx23cm baking tin with baking paper. Ensuring the baking paper surpasses the edge of the baking tin will make removing the brownies easier.
Cut the butter into cubes and microwave for 30 second intervals until fully melted. Add the chopped chocolate to the warm melted butter and stir until fully melted. Set aside.
In a large bowl, add the eggs, sugar, salt and vanilla essence. Using an electric whisk, beat the mixture until pale in color and fluffy, about 4-5 minutes.
Add the melted butter and chocolate mixture to the whipped egg mixture and mix gently until combined.
Sift in the flour and cocoa powder. Mix gently until fully incorporated.
Pour the batter into the prepared baking tin and spread evenly. Bake for 25 minutes. Place the baked brownies in the fridge to cool whilst you prepare the tiramisu topping.
Add the cold mascarpone cream and cream to a large bowl. Using an electric whisk, whisk the mixture until just combined. Mix the instant coffee, salt and water together until dissolved. Add the coffee mixture to the cream. Whisk until stiff peaks form.
Remove the cooled brownies from the fridge and spread the tiramisu cream on top. Place in the fridge to set for 1 hour or until you're ready to serve.
Once you're ready to serve, gently loosen the edges, using the baking paper to lift the tiramisu brownies out of the mold. Use a sift to sprinkle a generous amount of cocoa powder on top before slicing and serving. Enjoy tastebud!