In a medium mixing bowl, combine the melted butter, room temperature egg, vanilla extract, and softened cream cheese. Whisk them together thoroughly until the mixture is smooth and well blended.
Gradually add the strawberry cake mix to the wet ingredients, pouring in about half a box at a time. Mix gently until the cake mix is fully incorporated and a soft dough forms.
Carefully fold in the white chocolate chips and M&M's by hand, ensuring they are evenly distributed throughout your cookie dough.
For the best texture and easier handling, cover the dough and chill it in the refrigerator for at least one hour. If you're short on time, you can skip this step, but chilling helps prevent spreading.
Once the dough is chilled, preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for effortless cleanup.
Scoop out portions of the dough and roll them into small, 1-inch balls. Place these cookie dough balls onto the prepared baking sheet, leaving a little space between each.
Bake for 9 to 10 minutes. The cookies should appear set and slightly puffy, but avoid over-browning the tops.
Allow the cookies to cool on the baking sheet for a few minutes before carefully transferring them to a wire rack to cool completely. Enjoy these wonderfully moist and flavorful cookies!