Preheat your oven to 350 degrees F. Spray a 9" x 13" baking dish with nonstick spray. Line the bottom and sides with parchment paper. Spray again. Set aside.
In a medium size mixing bowl, whisk together the flour, cocoa powder, and salt. Set aside.
In a medium size saucepan, melt the butter and the bittersweet chocolate chips until smooth. Remove from the heat and allow to cool for about 5 minutes.
Add the brown sugar to the butter and chocolate mixture and stir until smooth.
Add the eggs, one at a time, stirring well between each addition.
Stir in the vanilla.
Add the flour mixture and stir until no streaks of flour remain.
Fold in the 1 cup of the semi-sweet chocolate chips.
Pour the batter into the prepared pan.
Bake the brownies for 15 minutes.
While the brownies bake, make the cookie dough. (Instructions below)
When the 15 minute timer is up, remove the pan from the oven. Pour the melted peanut butter on top and gently spread into an even layer.
Using your hands, break apart the cookie dough (instructions below) and drop on top of the peanut butter and brownie. This does not need to be spread out. It will spread as it cooks.
Evenly sprinkle the mini M&Ms on top.
Bake for 30 minutes more minutes.
The top of the cookie layer will be golden brown. Don’t let that scare you that it’s over cooked. The centers will still be gooey and you’ll get a delicious crunch with each bite, as well.
Remove the pan from the oven and sprinkle on the salt.
Allow the bars to cool in the pans for at least an hour.
The centers will still be gooey after they cool for an hour. If you want the centers more set, allow the bars to sit for an additional hour or two.