Grease a 9x13-inch baking pan with nonstick cooking spray. Set aside.
In a large pot, melt butter on low heat. You'll want to keep the heat low so that the butter melts but doesn't brown.
6 tablespoons salted butter
Once butter has melted, add the mini marshmallows.
16 ounce package mini marshmallows
Once marshmallows begin to melt, stir in the peanut butter. You'll need to stir the mixture constantly until the marshmallows have completely melted and everything is combined.
2/3 cup creamy peanut butter
Remove from heat.
Stir in the Rice Krispies.
7 cups Rice Krispies
Pour the cereal mixture into the prepared pan, and gently press it to form an even layer.
To make the topping, add the chocolate chips to a microwave-safe dish.
8 ounces semisweet chocolate chips
Microwave for 30 seconds. Stir.
Add the coconut oil, and continue microwaving and stirring in 15 second intervals until melted and combined.
1 teaspoon coconut oil
Pour the chocolate mixture over the bars, and spread to combine.
Let the treats set up and cool before serving.
Notes
Butter: You could also use unsalted butter and add a pinch of salt. The salt just helps to balance out the sweetness in the treats.
Marshmallows: Original (larger) marshmallows will also work.
Peanut butter: It's important to use regular peanut butter, like Jif or Skippy, and not natural peanut butter.
Chocolate chips: You can use dark chocolate chips or milk chocolate chips if you prefer.
Coconut oil: Shortening, like Crisco, can be used in place of the coconut oil.