Preheat the oven to 350F or 320F fan. Prepare a square baking dish, I used 8’’x8’’ and line it with parchment paper.

In a medium bowl, combine 1 cup of Greek yogurt with maple syrup and peanut butter.

Now, sift the oat flour and baking powder into the wet ingredients and mix throughout to combine and form a thicker batter. Add in the salt and mix it in.

Take 2/3 of the batter and add cocoa powder and leftover ¼ cup Greek yogurt to it. Add a splash of milk if the mixture is way too thick.

Add chopped chocolate to the remaining 1/3 of the batter. Combine them lightly. Leave a little bit of chocolate to sprinkle on the top of the brownie.

Cover the bottom of the baking dish with cocoa batter and level it out. Then, cover with the light batter and level it out. Use a knife to create a marble effect and then sprinkle with the remaining chopped chocolate.

Bake in the oven for 30 minutes. Remove and let it cool down inside the baking dish before slicing.