Preheat your oven to 325°F. Grease a standard 12-cup muffin pan.

To make the brownie batter, melt together chocolate and butter in a large heatproof bowl set over a pot with ½-inch of barely simmering water or in the microwave. Stir in cocoa powder and salt. Remove from heat and set aside to cool for 5 minutes.

In a separate medium bowl, whisk together whole egg, egg white and sugar until thickened and pale. Whisk in melted chocolate mixture. Sprinkle flour over batter and stir it in gently until you can no longer see it.

To make the cheesecake mixture, beat cream cheese in a medium bowl with a wooden spoon until smooth. Beat in sugar until glossy and then whisk in egg yolk and vanilla until creamy and smooth. Stir through yogurt and chocolate chips. Spoon about one tablespoon of brownie batter into each muffin hold. Divide cheesecake mixture among each muffin hole over the brownie batter. Spoon remaining brownie batter over the cheesecake mixture, dividing it equally (no need to spread it out).

Bake until slightly puffed and a toothpick inserted into the center comes out with a few moist crumbs, about 20 minutes. Let brownies cool completely in the pan before and then refrigerate for 1 hour before running a knife around the edges and removing from pan.