1. Get Ready to Bake: Preheat your oven to 350°F (175°C). Line a 9x9-inch baking pan with aluminum foil, making sure to leave an overhang for easy removal. Give the foil a light spray with cooking spray and set it aside.
2. Cream the Butter: In a large mixing bowl, beat the softened butter with an electric mixer on medium-high speed until it's wonderfully smooth and creamy.
3. Mix the Dough: Add the strawberry cake mix and the egg to the bowl. Beat on low speed until everything is well combined. Don't worry if the batter looks super thick at first; just keep mixing until it transforms from crumbly bits into a lovely, thick, and slightly sticky dough.
4. Create the Base: Press about half to two-thirds of the dough evenly into the bottom of your prepared pan. A spatula works well, or you can lightly spray your hands with cooking spray and gently press the dough into place. Set the remaining dough aside.
5. Add the Goodies: Generously sprinkle the white chocolate chips over the dough base.
6. Drizzle with Sweetness: Evenly drizzle about 8 ounces (or eyeball about 60% of the can) of sweetened condensed milk over the white chocolate chips. This is where the magic happens for that irresistible gooey texture!
7. Top it Off: Take the remaining dough and gently dot it in small, approximate 1-inch pieces over the sweetened condensed milk layer. Lightly press these pieces down. It's okay if it doesn't completely cover everything; the swirls will look beautiful.
8. Bake to Perfection: Place the pan in your preheated oven and bake for about 27 to 30 minutes. You'll know it's ready when the edges are set and the center looks mostly set, even if it has a slight wobble. The edges should be a light golden brown.
9. Cool for Gooey Perfection: This step is crucial for perfect slices! Let the bars cool completely on a wire rack for at least 2 to 3 hours. For the neatest squares, letting them cool overnight is even better. Slice and enjoy your delightful, homemade Valentine's treat!