Preheat the oven to 350°F and prepare an 8x8 inch baking pan by lining it with parchment paper or spraying it with non-stick spray.

In a microwave-safe bowl, melt the chopped dark chocolate.

Add the Greek yogurt and sugar, and whisk until smooth.

Add the flour, cocoa powder, and baking soda, and mix until combined.

Add the milk and mix well until smooth.

Fold in the chocolate chips if you are using them.

Pour the batter into the baking pan and bake for 25 to 30 minutes.

Remove from the oven and let it cool in the pan for 10 minutes before carefully transferring to a wire rack to cool completely.