Line an 8-inch square baking dish with parchment paper, allowing 1-inch wings to hang over the edges; set aside.
In a large pot over medium heat, melt the butter. Add the marshmallows and salt and cook, stirring, until the marshmallows are melted and smooth. Remove from the heat and stir in the peanut butter and vanilla (the peanut butter can still be swirly). Add the cereal, crushed graham crackers, chocolate chips and sprinkles and fold with a large rubber spatula to combine.
Pour the mixture into the prepared baking dish, using the spatula to spread it out evenly. Place a piece of parchment on top and then use your hands to press the mixture down very firmly. Top with additional sprinkles as desired. Let the mixture firm up in the refrigerator for 1 hour, then cut into squares.