Start by greasing a 9x13 inch baking pan with a little butter or lining it with parchment paper. This will prevent the treats from sticking and make it easier to lift them out later.
In a large saucepan over medium heat, melt the 5 tablespoons of unsalted butter. Stir gently until fully melted and bubbly.
Once the butter is melted, add in the 16 ounces of miniature marshmallows and stir continuously until they are completely melted and smooth. This should take about 3-5 minutes. Be careful not to let the mixture burn!
Remove the saucepan from heat and stir in the 1/4 teaspoon of salt and 1 teaspoon of vanilla extract. This step enhances the flavors and balances the sweetness of the marshmallows.
Gently fold in the 4 cups of Fruity Pebbles cereal and 2 cups of Rice Krispies cereal. Make sure all the cereal is evenly coated with the marshmallow mixture.
Pour the mixture into the prepared baking pan. Using a spatula or your hands (greased with butter to prevent sticking), press the mixture down firmly and evenly into the pan. Be careful not to pack it too tightly, as you want the treats to remain light and chewy.
Allow the treats to cool at room temperature for about 30 minutes or until they are set. Once cooled, you can cut them into squares or rectangles.
