Lightly grease a 9×9-inch baking dish and a spatula or your hands with a little of the butter; set the dish aside. Crush the 8-oz. bag of Ruffles (in a sealed plastic bag or food processor) until you have 6 cups crushed, then transfer the crushed chips to a large bowl and set aside.
In a large pot over medium-low heat, melt the 3 tablespoons butter.
Add the 4 1/2 cups mini marshmallows to the melted butter and stir constantly over medium-low heat until the marshmallows are completely melted and smooth.
Remove the pot from the heat and stir in the 1 teaspoon vanilla extract.
Add the 6 cups crushed Ruffles to the melted marshmallow mixture and fold gently until the chips are evenly coated.
Pour the mixture into the greased 9×9 dish and press it evenly and firmly into the pan using the greased spatula or greased fingers.
Let the treats cool to room temperature until set, then cut into squares and serve.