Line a 9 by 13-inch rectangular baking pan with parchment paper, allowing some to hang off the sides to make it easier to grab, and grease with cooking spray.

In large pot or dutch oven, set over medium heat, melt the butter and cook until brown bits form at the bottom. Keep an eye on it and make sure that it doesn't burn. Once the splattering subsides and the butter has browned evenly, add the mini marshmallows (reserving the 1 1/2 cups for later). Stir until melted through, about 3 to 4 minutes. Remove from heat and add the rice cereal. Stir until well combined. Add the reserved mini marshmallows and fold in. Transfer the marshmallow cereal mixture to the prepared baking pan and spread out into an even layer. Using wet hands, press down on the mixture to compact it. Set aside.

In a medium saucepan, combine the condensed milk, brown sugar, butter and milk. Set over medium-high heat and cook until melted through. Bring to a boil, and continue to stir nonstop and cook for about 5 minutes. Remove from heat and stir in the vanilla extract and peanuts. Pour the mixture over the rice cereal layer and spread out evenly with a spatula. Place in the fridge or freezer to let set, about 30 minutes.

Meanwhile, fill a medium saucepan halfway with water and bring to simmer. Place a bowl over the top, making sure the water doesn't touch the bottom of the bowl. Add the chocolate and stir until melted through. Remove from the double boiler and stir in the oil. Pour the melted chocolate over the caramel peanut layer and spread out evenly with an offset spatula. Return to the fridge or freezer to allow the chocolate to set.

Remove the bars from the pan and cut into 24 pieces. Leftovers can be kept in the fridge for up to 4 days. Enjoy!