Line the baking dish with parchment paper and brush the sides with some melted butter.
In a bowl sift flour, baking powder, salt and cocoa powder together. Add Sugar and keep aside.
In another bowl, add melted (cooled) butter, yogurt, milk and vanilla extract. Mix till all the ingredients are combined well.
Add the dry mixture from point #3 above to wet ingredients and fold gently. Do not over mix. The mixture will be on the thicker side. Add in walnuts and choco chips and fold again.
Pour the mixture into prepared baking dish and bake for 40 mins. Insert a toothpick or fork at 35 min to check if the brownie is ready or still needs more baking. If the toothpick or fork comes out clean, the baking is done.
Once done, cool completely, invert on a metal rack and cut into pieces.
Serve with ice cream, chocolate sauce or have it as it is!
You can add choco chips for added flavor along with walnuts