Preheat your oven to 350°F (175°C).
Line your 9x13 inch baking pan with parchment paper, leaving some overhang on the sides.
In a large mixing bowl, combine the white cake mix, eggs, and vegetable oil. Mix until just combined.
Pour in the sweetened condensed milk and mix until the batter is smooth.
Gently fold in the semisweet chocolate chips.
Pour the batter into the prepared baking pan and spread it out evenly.
Dot the top of the batter with the cubed salted butter.
Bake for 25-30 minutes, or until the edges are golden brown and a toothpick inserted in the center comes out with a few moist crumbs.
Allow the bars to cool in the pan for about 10 minutes. Lift them out using the parchment paper and let cool completely on a wire rack before cutting into squares.
