Instructions

• Preheat the oven to 350°F (175°C) and grease a 9×13-inch baking dish.
• In a large bowl, stir together the white cake mix, the 2 large eggs, and the 1/3 cup vegetable oil until well combined; the batter will be thick.
• Transfer about 2/3 of the batter to the prepared baking dish and press it evenly to completely cover the bottom.
• In a microwave-safe bowl, combine the 14-ounce can of sweetened condensed milk, the heaping cup of semisweet chocolate chips, and the 1/4 cup cubed salted butter. Microwave for 30 seconds, stir; microwave an additional 20 seconds, stir; if the chocolate chips and butter are not fully melted, microwave another 20 seconds and stir until the mixture is smooth.
• Pour the chocolate-condensed milk mixture evenly over the pressed batter in the baking dish.
• Drop the remaining batter by small spoonfuls over the chocolate layer (it’s fine if there are gaps).
• Bake for 20 to 24 minutes, until the edges are set and a toothpick inserted into a cake portion comes out mostly clean.
• Let the pan cool until the bars are firm, then cut into squares.