Spray a 9x13 inch baking dish with nonstick cooking spray, or grease with butter. Set aside.
Melt the butter in a large pot over medium heat until melted, then reduce the heat to low and stir in 15 ounces of the marshmallows.
Stir in the peanut butter. Stir continuously until the marshmallows and peanut butter melt completely. Remove from heat, then stir in the vanilla extract.
Pour in the Rice Krispies cereal and stir until about halfway mixed. Then stir in the remaining marshmallows. Mix until the marshmallows are evenly distributed.
Transfer the mixture to prepared dish. Make sure not to compress the mixture, which will lead to dense treats. Sprinkle a pinch of flaky salt evenly over the bars. Let set and cool for 30 minutes before cutting.
Storage - Store these in an airtight container at room temperature for about 3 days. These bars don’t necessarily need to be refrigerated because they’ll get hard, however, you can freeze a batch and reheat it when you want them. Freezing will allow them to last for about a month and a half!
Calories: 232kcal | Carbohydrates: 35g | Protein: 3g | Fat: 10g | Saturated Fat: 4g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 4g | Trans Fat: 0.2g | Cholesterol: 12mg | Sodium: 160mg | Potassium: 72mg | Fiber: 1g | Sugar: 18g | Vitamin A: 887IU | Vitamin C: 7mg | Calcium: 8mg | Iron: 4mg