Preheat the oven to 180°C, and grease + line a 9-inch brownie tin with parchment paper. Prepare the cream cheese by cutting it into thin slices - we're not looking for perfection here - and returning it to the fridge for now.
In a medium pot, melt the chocolate and butter together over a medium-low heat. Nigella doesn't bother with a bain-marie, so I followed her lead and nothing terrible happened. When melted, set aside to cool slightly.
In a medium bowl, use a whisk to lightly beat together the sugar, eggs, and vanilla.
Pour the melted chocolate mixture into the egg mixture in a slow steady stream, whisking all the while.
Measure the flour directly into the bowl, and whisk until no lumps of flour remain.
Pour half of the batter - by eye is fine - into the prepared brownie tin, spread the sliced cream cheese evenly over the top of it, and then cover the cream cheese with the remaining batter. Use a spatula to spread the top batter around, ensuring the cream cheese is covered.
Bake in the preheated oven for 20-25 minutes, or until the top is papery but a skewer inserted into the centre comes out "still-sticky". Cool in the tin for 10-minutes before moving to a wire rack to cool completely. Slice and enjoy!