Coat the inside of a 9-inch x 13-inch baking pan with non-stick cooking spray.
In a medium mixing bowl, mix together cake mix, eggs, oil, and caramel extract until batter is smooth.
Stir in most of the chocolate chips and 1/2 cup of the mini marshmallows. The rest of the chocolate chips will go on top.
Press the mixture into your prepared pan with the back of a wooden spoon or your hands. It will seem like a very thin layer, but that is what you're looking for.
Top batter with remaining chocolate chips and mini marshmallows.
Chill batter in the fridge for 20 minutes. In the meantime, preheat your oven to 350 degrees F.
Remove the pan from your fridge and place it on the middle rack of your oven. Bake for 18-20 minutes. When the cookies are done the edges will be just set and the cookie will look a bit puffy and still be soft.
Remove from oven and let cool completely. (The cookies will firm up as they cool.) Cut into 20 bars and enjoy! Store any leftovers in an airtight container for up to 1 week.
Notes
DO NOT skip the chill time for these cookie bars. This is what helps them have a cookie texture instead of being more cakey once baked.These cookies have a tendency to fall apart if cut while still warm. Let them cool all the way before cutting.