Preheat the oven to 180C/350F. Line a 5" (14 cm) square pan with parchment paper, and set aside.

In a microwave-safe bowl, melt your chopped chocolate. Let sit for 1-2 minutes, before adding your yogurt and sugar. Whisk until smooth and transfer to a large mixing bowl.

Add the flour, cocoa powder, and baking soda, and mix until just combined. Add your milk and mix well, until fully incorporated. Fold through your chocolate chips, if using them.

Transfer to the lined pan and bake the brownies for 27 minutes, or until a skewer comes out tiny bit wet. Remove from the oven and let cool in the pan for 10 minutes, before carefully transferring to a wire rack to cool completely. Use a hot knife to cut into 9 squares. Enjoy!