Preheat your oven to 350°F (175°C). Line a 9x9-inch baking pan with aluminum foil and spray with cooking spray.

In a large mixing bowl, cream the unsalted butter until smooth and creamy, about 1-2 minutes.

Add the entire box of strawberry cake mix and the egg, mixing on low speed until a thick dough forms, about 1-2 minutes.

Press half to two-thirds of the dough into the prepared pan to create a base layer.

Sprinkle the white chocolate chips evenly over the pressed dough.

Drizzle the sweetened condensed milk over the chips.

Crumble the remaining dough over the chocolate layer.

Bake for 27-30 minutes until the edges are set and the center is slightly jiggly.

Allow the bars to cool in the pan for 2-3 hours before slicing.