Preheat your oven to 350°F (175°C). This ensures that your cookies will bake evenly.
In a mixing bowl, use an electric mixer to beat together the softened butter and granulated sugar until the mixture is light and fluffy, about 2-3 minutes.
Add the eggs one at a time, mixing well after each addition. Then, stir in the vanilla extract until fully combined.
In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt. This ensures even distribution of the dry ingredients.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Be careful not to overmix, as this can lead to tough cookies.
Gently fold in the semi-sweet chocolate chips and mini M&Ms with a spatula, ensuring they are evenly distributed throughout the dough.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto a baking sheet lined with parchment paper, spacing them about 2 inches apart.
Press a few extra M&Ms onto the top of each cookie dough ball for a pop of color and extra sweetness.
Bake in the preheated oven for 10-12 minutes, or until the edges are set but the centers are still slightly soft. They will continue to firm up as they cool.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. Enjoy your Double Chocolate M&M Cookies with a glass of cold milk or your favorite beverage!