Put yogurt, eggs and oil in a large bowl and give them a good whisk. Add brown sugar and whisk until nice and smooth (the mixture will be the colour of caramel). Set aside.
In another bowl weigh out all your dry ingredients (flour, cocoa and baking powder). Sift these directly onto the wet ingredients and mix in gently only until all the dry ingredients are fully incorporated (do not overmix). Add chocolate chips and fold them in gently.
Prepare cream cheese mixture by whisking cream cheese with egg, sugar and vanilla until nice and smooth.
Preheat the oven to 180C/350F/Gas Mark 4. Fill 12 muffin cases half way up with chocolate muffin batter. Follow with cream cheese mixture (divide it evenly in between 12 muffin cases - approx. 2 heaped teaspoon per muffin). Follow with a small dollop of remaining chocolate batter mixture on top of cheese mixture. You can bake these as they are or using a toothpick swirl cheese and chocolate mixture around a bit. Bake for 20-25 minutes until the skewer inserted in the centre of the muffins comes out clean. Remove to the cooling rack to cool completely and enjoy!
Notes
Calories are approximate and per muffin
Feel free to replace dark chocolate chips with milk or even white chocolate ones for sweeter, less savoury flavour