Preheat oven to 350 degrees F. Line a 9-inch square baking dish with parchment paper. Set aside.
In a medium sized saucepan, melt butter over medium heat. Remove from heat and add in 0.5 cup of the semi-sweet chocolate morsels with the sugar. Stir until combined and morsels are melted.
Add in eggs, one at a time, stirring after each addition.
Add in vanilla extract.
Add cocoa powder, flour, salt, and baking powder. Using big stroked, stir JUST until combined and no longer see dry ingredients.
Fold in remaining semi-sweet morsels and 0.5 cup of the M&M's candies. Pour batter into the prepared baking dish.
Sprinkle the top with the remaining M&M's candies.
Bake for 38 minutes. Remove from oven and cool COMPLETELY before cutting.
Notes
Wait for brownies to cool completely before slicing to prevent them from falling apart.