Preheat the oven to 350 degrees Fahrenheit and spray a 9x13-inch baking pan with baking spray.

Mix the chocolate cake mix, eggs, melted butter, and heavy cream in a large bowl until well combined. The mixture will be thick.

Fold in the dark and milk chocolate chips until evenly distributed.

Spread the mixture into the prepared baking pan in an even layer.

Bake for 23-26 minutes or until a toothpick inserted in the center comes out with some goo but not covered in batter.

Remove from the oven and cool completely before cutting into squares and serving.