Line a 9×9-inch pan with parchment paper, leaving overhang for easy removal.
Combine graham cracker crumbs, melted butter, condensed milk, and vanilla until evenly mixed.
Press mixture into the pan base firmly for a solid crust.
Sprinkle white chocolate chips, marshmallows, and sprinkles over the crust.
Refrigerate for at least 2 hours or until firm.
Lift using parchment, cut into squares, and serve chilled.
