Cut parchment paper to fit the bottom of a 9-inch, spring-form pan. Spray the sides and bottom of the pan, the put the parchment paper inside. Spraying the bottom helps the parchment paper adhere to the pan.
Mix the dry ingredients in a bowl
In a separate bowl, cream together the butter and peanut butter
Add the eggs one at a time, mixing thoroughly after each addition
Add the sugars in 3-4 increments, mixing thoroughly after each addtion.
Add half the flour mixture and mix at medium to low speed
Add the remaining flour mixture and continue mixing
Add the M&Ms
Place in prepared pan and bake for 30-35 minutes. A toothpick will come out clean when the brownies are done.
Let cool at least ten minutes before removing from pan
Notes
Of course, you can make these in a conventional 8x8 baking pan, in which case you can either omit the parchment paper or use it to line the entire pan. See the above brownie recipe for comments.