Preheat Oven: Preheat oven to 350°F (175°C) and line a 9×9-inch pan with aluminum foil (for easier cleanup) and spray with cooking spray; set aside.

Cream Butter: In a large bowl, beat the softened butter with an electric mixer on medium-high speed until smooth and creamy.

Mix Dough: Add the strawberry cake mix and egg, and beat on low speed until the batter forms a thick, tacky dough. Keep mixing until it’s smooth.

Create Base Layer: Press half to two-thirds of the dough into an even layer in the prepared pan. Use a spatula or your hands (sprayed with cooking spray) to make it smooth; set remaining dough aside.

Add Filling: Evenly sprinkle white chocolate chips over the dough. Drizzle about 60% of the sweetened condensed milk (about 8 ounces) evenly over the top.

Top Layer: Crumble the remaining dough into 1-inch pieces and scatter over the condensed milk, lightly pressing down. You don’t need complete coverage.

Bake: Bake for 27-30 minutes, or until the edges are golden brown and the center is mostly set. It’s okay if the center is slightly jiggly.

Cool: Allow the pan to cool on a wire rack for at least 2-3 hours (overnight is even better) until the bars are firm enough to cut.

Serve: Slice into 16 bars and enjoy!