Preheat oven to 350 degrees F. and line an 8×11 inch baking dish with foil that has been sprayed with cooking spray.
Place butter into a large mixing bowl and microwave until melted and hot, about 45 seconds or so. Pour in chocolate chips and stir until mostly melted. It’s ok, if it’s not perfectly smooth. Add flour, salt and sugars. Mix a few times then add egg yolks and oil. Mix until well combined then add pecans.
Transfer half of the batter to prepared baking dish, spreading evenly. Top with marshmallows and drizzle with caramel sauce. Top with remaining brownie batter. Bake for 55-60 minutes, until cooked through. Let cool completely before cutting into squares.