Start by greasing your 9x13 inch baking pan with a little butter or lining it with parchment paper.
In a microwave-safe bowl, combine the stick of salted butter and the 26 ounces of mini marshmallows. Microwave on high for about 1 to 2 minutes, stirring halfway through, until melted and smooth.
Once melted, stir in the teaspoon of vanilla extract.
In a large mixing bowl, add the 10 cups of Golden Grahams cereal. Pour the melted marshmallow mixture over the cereal and fold until evenly coated.
Fold in the 2 cups of mini peanut butter cups until evenly distributed.
Pour the mixture into the prepared baking pan and press firmly to create an even layer.
Allow to cool at room temperature for about 30 minutes or place in the fridge to speed up the setting process. Cut into squares once set.