Preheat & Prep:
Preheat the oven to 350°F (175°C) and grease a 9x13-inch baking pan or line it with parchment paper.
Make the Batter:
In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth.
Add the eggs and vanilla extract, whisking until well combined.
Sift in the cocoa powder, flour, salt, and baking powder. Stir gently until just incorporated.
Add the M&M’s:
Fold in the M&M’s and chocolate chips (if using).
Bake:
Pour the batter into the prepared pan, spreading it evenly. Sprinkle additional M&M’s on top.
Bake for 30-35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Cool & Serve:
Let the brownies cool completely before slicing. Enjoy warm for a gooey texture or at room temperature for a firm bite!