Prepare Dry Ingredients: In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt until well combined. Set aside.

Cream Butter and Sugars: In a large bowl, beat together butter, granulated sugar, and brown sugar on medium speed for about 3-5 minutes until creamy.

Incorporate Eggs and Vanilla: Add eggs one at a time, mixing well. Then, add vanilla and mix for an additional minute.

Combine Mixtures: Gradually add dry ingredients to the creamed mixture, folding gently until just combined.

Portion Cookie Dough: Use a cookie scoop to take about 2 ounces of dough for each cookie, roll into balls, and flatten slightly on a baking sheet.

Add M&M's: Press a handful of M&M's into the tops of each dough ball.

Bake Cookies: Preheat oven to 350°F (175°C) and bake for 9 to 11 minutes. Allow to cool on sheet for 5 minutes before transferring to a wire rack.