Refrigerate the dough for at least 30 minutes before baking to prevent spreading and achieve chewy, bakery-style cookies with defined edges.

Bring eggs and milk to room temperature before mixing to ensure smooth incorporation and a more uniform, tender crumb structure throughout.

Mix just until the dry cake mix is incorporated—overmixing develops gluten and creates tough, dense cookies instead of soft, chewy ones.

Add rainbow sprinkles and mini chocolate chips in the final step after mixing to prevent color bleeding and keep them vibrant and intact during baking.

Remove cookies from the oven when the edges are set but the centers still look slightly underdone—they'll continue cooking on the hot baking sheet for perfect chewy texture.