Begin by lining a 9x13-inch baking pan with aluminum foil or parchment paper, ensuring it hangs over the edges for easy lifting later. Lightly spray the lining with nonstick cooking spray to prevent sticking.

In a large pot over medium-low heat, add ½ cup of unsalted butter. Stir in 1 cup of creamy peanut butter, mixing until you achieve a smooth, velvety texture.

Add 15 ounces of marshmallows and stir continuously until everything is melted and forms a gooey mixture, about 3-5 minutes.

Remove from heat and stir in 1 teaspoon of vanilla extract until thoroughly mixed.

While the mixture is still warm, fold in 6 cups of Rice Krispies cereal, ensuring each piece is evenly coated without crushing the cereal.

Transfer the mixture into your prepared pan, pressing down firmly and evenly until it fills the pan.

Allow to cool at room temperature for about 30 minutes until firm to the touch. Once set, lift out using the edges of the foil or parchment and slice into bars.