Preheat your oven to 350°F (175°C).
Grease your 9x13 inch baking pan with cooking spray or line it with parchment paper.
In a large mixing bowl, combine the yellow cake mix, eggs, melted butter, vanilla extract, and milk. Mix well until smooth.
Gently fold in the Andes mint chips and dark chocolate chips into the batter.
Pour the batter into the prepared baking pan and spread it out evenly.
Place the pan in the oven and bake for 25-30 minutes until the edges are lightly golden.
Let the cookie bars cool in the pan for about 10-15 minutes before transferring them to a cooling rack.