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

In a large mixing bowl, beat the softened unsalted butter until creamy, then gradually add the strawberry cake mix and egg, mixing until well combined.

Press approximately two-thirds of the dough evenly into the prepared baking pan, smoothing it out for an even surface.

Sprinkle the white chocolate chips over the pressed dough and drizzle the sweetened condensed milk on top.

Use the remaining dough to create dollops over the milk, allowing for pockets of gooey texture.

Bake for 27-30 minutes until the edges are set and golden, while the center remains slightly jiggly.

Allow the bars to cool in the pan for 2-3 hours or overnight before lifting them out and cutting into squares.