01 -
Position two racks near the center of your oven and preheat to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats to prevent sticking and for easy cleanup.
02 -
In a large mixing bowl, whisk together the yellow cake mix and baking powder until well combined. This step helps distribute the baking powder evenly throughout the cake mix for consistent leavening.
03 -
In a separate glass measuring cup or small bowl, whisk together the room temperature eggs, oil, and vanilla extract until smooth and well blended. Room temperature eggs incorporate more easily into the batter and help create a better texture.
04 -
Pour the wet egg mixture into the bowl with the dry cake mix. Stir thoroughly until a soft dough forms, making sure to work out all flour pockets for a smooth, consistent dough. Gently fold in the mini chocolate chips, M&Ms, and if using, the rainbow jimmies and nonpareils, distributing them evenly throughout the dough. Allow the dough to rest for 10 minutes, which helps the dry ingredients fully hydrate and makes the dough easier to handle.
05 -
Using a cookie scoop or spoon, portion approximately 2 tablespoons of dough for each cookie. Roll the dough between your palms to form oval-shaped balls that are taller than they are wide (this helps create thicker, softer cookies). Place the dough balls on the prepared baking sheets, spacing them about 2 inches apart to allow for spreading. If desired, press a few additional M&Ms and chocolate chips onto the tops of the cookie dough balls for a more colorful appearance.
06 -
Bake the cookies in the preheated oven for 10-11 minutes. The cookies should be set at the edges but still soft in the center. It's important not to overbake—the cookies should not brown, which would make them too crisp. They'll continue to firm up as they cool.
07 -
Allow the cookies to cool on the baking sheets for at least 3-5 minutes; they'll be too fragile to move immediately after baking. If the cookies are very puffy, gently press down on the tops with the back of a spoon to flatten them slightly. After the initial cooling period, carefully transfer the cookies to a wire rack to cool completely. The cookies will firm up as they cool while maintaining their soft, cake-like interior.