Line an 8-inch square baking pan with parchment paper, leaving 2 inches on either side.
In a sauce pan over medium low heat, put butter, chocolate chips, condensed milk and vanilla. Continue cooking until chocolate chips are melted, stirring frequently (about 8 to 10 minutes).
Remove from heat and stir in 2 cups potato chips.
Pour mixture into prepared baking dish, smoothing out the top. Sprinkle the top with remaining potato chips (note: it helps to gently press the potato chip topping into the fudge mixture into the mixture to help them stick).
Refrigerate for 2 hours to overnight (covered). Remove from refrigerator and cut into squares.
Recipe by Alida's Kitchen at https://www.alidaskitchen.com/2015/06/24/potato-chip-fudge-recipe/