1-Preheat the oven to 180C/350F: Preheat the oven to 180C/350F. Line an 8 x 8-inch pan with parchment paper, and set aside.
2-In a microwave-safe bowl, add your chopped: In a microwave-safe bowl, add your chopped chocolate. Melt your chocolate. Let sit for 1-2 minutes, before adding your yogurt, vanilla, and sugar. Whisk until smooth and transfer to a large mixing bowl.
3-Add the flour, cocoa powder, and baking: 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.
4-Transfer to the lined pan and bake: Transfer to the lined pan and bake the brownies for 25-30 minutes, or until a skewer comes out just clean. Remove from the oven and let cool in the pan for 10 minutes, before carefully transferring to a wire rack to cool completely.