Preheat oven to 350 degrees and line a 9x13 inch baking pan with foil. Grease foil with cooking spray and set aside.
First prepare the brownie batter. Combine chocolate chips and butter in a large sauce pan and stir over medium heat until completely melted and combined. Transfer mixture to a large mixing bowl and whisk in 3 eggs, granulated sugar, 2 tablespoons brown sugar, and vanilla extract. Allow to cool for 10 minutes.
In a medium bowl whisk together flour, baking powder, 1/2 teaspoon salt, and cocoa powder. Add dry ingredients to wet ingredients and stir til combined. Reserve and set aside 1 cup of the batter. Spread remaining batter in the bottom of your prepared baking pan.
In another bowl whisk together pumpkin, remaining 3 eggs, 1/2 cup heavy cream, remaining 1/3 cup brown sugar, remaining 1/2 teaspoon salt, and pumpkin pie spice. Pour mixture over brownie batter in pan.
In a microwave safe bowl combine caramels and remaining 1/4 cup heavy cream. Cook on high for 2 minutes, stir, and return to microwave for 20 seconds at a time (stirring after each) until caramel is melted and smooth. Drizzle caramel over pumpkin batter.
Drop spoonfuls of reserved brownie batter over caramel and pumpkin layers. Use a butter knife to swirl layers (creating a figure-8 a few times usually does the trick).
Bake for 45-50minutes until an inserted toothpick comes out clean (a few crumbs are okay but no wet batter). Allow to cool completely before cutting into bars and serving.