01 -
First, heat your oven to 350°F. Cover a 9×9-inch baking pan with foil for easier cleanup, then spray it generously with cooking spray.
02 -
Using an electric mixer on medium-high, beat your softened butter until it's completely smooth and creamy.
03 -
Add the egg and cake mix to your butter. Start mixing at a low speed. When the dough becomes sticky and thick with small crumbs, you're good to go!
04 -
Take about two-thirds of the dough and push it down evenly in the pan to make a flat bottom layer. Evenly toss the white chocolate chips over it, pour the condensed milk all over, then scatter pieces of the leftover dough (about an inch in size) on top. Gently press them down a little.
05 -
Pop it in the oven for 27-30 minutes. You'll know it's ready when the edges look lightly golden, and the center looks set but still wiggles a tiny bit.
06 -
Cool the bars on a wire rack for no less than 2-3 hours. Overnight cooling is even better to get the perfect texture for cutting.