Preheat the oven to 350 degrees Line a 9x13 inch baking dish with foil and spray it with cooking spray.
In a large bowl combine butter and cocoa powder. Mix well. Add the granulated and brown sugars. Mix in well. Add the eggs, one at a time, and mix into the batter into well incorporated. Add the flour and mix well. Gently stir in m&m’s.
Pour the mixture into the prepared baking dish and spread the batter evenly if needed.
Place into the oven and bake for 30-35 minutes r until the edges pull away slightly from the pan and the center is done.