Preheat the oven to 350°F. Line a 9x13 inch baking pan with parchment paper. Set aside.
Add the melted butter, oil and sugars to a medium bowl. Whisk well, then add the eggs and vanilla. Whisk for 2 additional minutes.
Sift together the flour, cocoa, salt and baking powder into a separate bowl.
Pour the dry mixture into the bowl with the wet mixture. Fold the ingredients until just combined.
Add 1/2 c chocolate chips, 1/4 c mini M&M's and 1/4 c regular M&M's and fold into the batter until evenly distributed.
Pour the batter into the lined baking pan. Sprinkle the remaining M&Ms evenly over the top.
Bake for 25-30 minutes or until the center is cooked through and no longer jiggles.
Allow the brownies to cool in the pan before lifting them out and cutting.
Tip: Use a plastic knife to cut the brownies. It'll slice right through them.