Prepare the Batter

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking pan or line it with parchment paper.
2. Melt the Butter: In a microwave-safe bowl, melt the butter and let it cool slightly.
3. Mix the Sugars and Eggs: In a large mixing bowl, combine the melted butter, granulated sugar, and brown sugar. Beat in the eggs one at a time, then stir in the vanilla extract.
4. Combine Dry Ingredients: In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt.
5. Make the Batter: Gradually fold the dry ingredients into the wet mixture, stirring until just combined. Be careful not to overmix.

Assemble and Bake

1. Pour the Batter: Spread the brownie batter evenly into the prepared pan.
2. Add M&M’s: Sprinkle M&M’s evenly over the top of the batter, pressing them gently so they stick.
3. Bake: Bake in the preheated oven for 28–32 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
4. Cool: Allow the brownies to cool in the pan for at least 10 minutes before slicing.