Preheat your oven to 300 degrees F. This step is crucial as it ensures that your cookies bake evenly. While preheating, line two large baking sheets with parchment paper. A light spray of non-stick spray will help the cookies not stick, making your cleanup a breeze.
In a medium-sized bowl, whisk together all-purpose flour, cocoa powder, baking powder, and salt. Mixing these dry ingredients first allows for an even distribution of the leavening agent and ensures your cookies rise perfectly.
Next, in a large, microwave-safe bowl, combine semi-sweet chocolate chips and unsalted butter. Heat them in the microwave on low power for 15-second increments, stirring in between each session until melted. Make sure the mixture is smooth and glossy; if you overheat it, the chocolate will seize and become grainy.
Once melted, whisk in pure vanilla extract, followed by the granulated sugar and light brown sugar. The mixture should be shiny and smooth, indicating the sugars are well incorporated.
Beat in eggs one at a time, ensuring to whisk well after each addition. This step incorporates air into the batter, making your cookies light and fluffy. After the eggs, mix in whole milk to bring everything together.
Add the dry ingredients you set aside earlier into the wet mixture. Stir gently to combine, ensuring not to overmix. The dough should come together as a cohesive mixture, but some lumps are okay!
Now it’s time to fold in the fun! Add the milk chocolate M&Ms and milk chocolate chips, stirring until evenly distributed throughout the dough.
Scoop generous 1/4 cupfuls of dough onto your prepared baking sheets, spacing them about 2 inches apart. This will give them plenty of room to spread. The dough may seem a bit thick, but that’s exactly what you want for chewy cookies.
Bake one tray at a time for 16 to 18 minutes. You’ll know they’re done when the edges are set, and the tops look dark and shiny. It’s tempting to open the oven early, but resist! This helps achieve that perfect soft center.
As soon as they come out of the oven, gently press a few extra M&Ms and chocolate chips into the tops of the warm cookies for added decoration. Allow them to cool completely on the baking sheet before serving to ensure they hold their shape.