Preheat the oven to 180°C. Line an approx. 20x20 cm cm baking tray with parchment paper.
Melt the butter and chocolate over simmering water, then pour in the coffee. Let it cool.
Mix in the sugar, vanilla, and a pinch of salt.
Whisk the egg, then stir it into the chocolate sauce. Sift in the flour, slowly and gradually, while combining gently.
In another bowl, beat the cream cheese until fluffy, then mix in the sugar, vanilla and egg.
Pour the chocolate mixture into the baking tray, spreading it out with a flat wooden spoon. Add the cream cheese batter and create marble patterns with a flat knife.
Bake for 30 minutes - but don't overbake, the middle of the cake should remain slightly gooey!
Let it cool in the tin for 15 minutes, then turn it out onto a wire rack.
Let it cool completely, before slicing it into cubes. You might want to chill it in the fridge for a couple of hours before slicing.
Serve with icing sugar dusted on top (optional).