Preheat oven 176c | 350F. Spray a 9-13-inch baking tray with oil spray, wipe over with a paper towel, and set aside.
Whisk flour, cocoa powder, sweetener, sugar and baking powder until combined.
In a separate bowl, whisk the butter/oil, yoghurt, egg, vanilla and milk until combined.
Pour into the dry ingredients and mix well with a wooden spoon (being careful not to over beat).
The batter should be smooth, creamy and lump free.
Fold through crushed cookie pieces.
Pour batter into baking tray and bake for 25 - 30 minutes, or until a toothpick inserted into the centre comes out clean. (my toothpick came out a little 'dirty' when I took them out after 30 minutes, and they were beautiful, moist and fudge-y).
While brownies are baking, make creamy frosting!