Pre-heat the oven to 170°C (325ºF).
Prepare a fairly large square/rectangle baking tin by lining it with baking paper or by greasing.
Slowly heat the chocolate and butter in a pan until just melted, then add in the coffee (or milk)
In a large bowl, whisk sugars together with the eggs, then add in the cooled chocolate mixture.
Sift the vanilla sugar, flour and cocoa and stir into the wet ingredients until just combined.
Pour half of the batter into the prepared pan.
Dollop the caramel/dulce de leche over the top, then cover with the remaining batter.
Bake for around 20-22 minutes (see note 2).
Remove from the oven and either allow it to cool completely or serve it warm with ice-cream. Enjoy!