In a large bowl, add the melted butter, sugar, brown sugar, and cocoa powders. Mix well with a whisk until fully combined.
1 cup butter, 1 cup sugar, 1 cup brown sugar, ½ cup cocoa powder, ¼ cup dark cocoa powder
Add eggs, one at a time, whisking between each addition.
Add in the salt, vanilla, baking powder, and baking soda. Whisk until combined.
¼ teaspoon salt, ½ teaspoon baking soda, ½ teaspoon baking powder, 1 teaspoon vanilla
Add in the flour and stir gently with a spatula until fully combined.
2 ½ cups flour
Add in the chocolate chips and ½ cup of M&Ms. Stir to combine.
½ cup chocolate chips, ½ cup M&Ms + more for pressing into tops of cookies
Cover and refrigerate for at least 30 minutes (I left mine overnight).
Once ready to bake, preheat oven to 350 degrees, line cookie sheets with parchment paper, then use a cookie scoop to drop 12 balls of dough per sheet.
Press more M&Ms into the tops of the cookie balls.
Bake for 9-12 minutes, remove from oven, let cool for a couple minutes on the baking sheet then transfer to a wire rack to fully cool.