Preheat your oven to 170°C fan / 180°C conventional and line a square baking tin with parchment paper.
Melt the chocolate and butter
Place the unsalted butter, milk chocolate and dark chocolate in a microwave-safe bowl and melt in 30 second intervals, stirring between each interval until smooth.
Add the brown and white sugar
Transfer the melted mixture to a large mixing bowl and whisk in the white sugar and brown sugar until fully combined.
Add the eggs and flavourings
Crack in the four eggs, then add the vanilla extract and a pinch of sea salt. Whisk until the mixture becomes smooth and glossy.
Add the dry ingredients
Sift in the cocoa powder and plain flour and gently fold everything together with a spatula until fully combined.
Bake the brownies
Pour the brownie batter into the prepared tin and spread it evenly. Bake for 25–35 minutes, depending on how fudgy you prefer your brownies. The edges should be set while the centre stays slightly soft.
Allow the brownies to cool
Remove the brownies from the oven and allow them to cool completely in the tin.
Prepare the espresso layer
Brew strong espresso or coffee and allow it to cool slightly. Dip the sponge fingers quickly into the espresso and arrange them in a single layer on top of the cooled brownie base.
Make the mascarpone cream
In a mixing bowl, whip the double cream, icing sugar and vanilla extract until soft peaks form. Add the mascarpone and gently fold until smooth and creamy.
Add the mascarpone topping
Spread the mascarpone cream evenly over the espresso-soaked sponge fingers.
Finish with cocoa powder
Dust the top generously with cocoa powder for the classic tiramisu finish.
Chill before slicing
Place the brownies in the fridge for at least 5 hours but overnight is best, before slicing so the layers set properly.