In your mixer, cream your butter and sugars until thick and smooth. Add in your eggs and vanilla essence and beat until combined. Add in your flour, baking powder and Bicarb. And mix until combined. Throw in the M&Ms and mix by hand. Roll into balls using 1 tsp of cookie dough. Lay on a tray and store in the freezer for 15 minutes. Preheat oven to 170c. Freeze for 15 minutes. Bake for 10 minutes, or until crisp and golden on the edges and slightly soft in the middle. Bake for an extra few minutes if you prefer a firmer cookie.