In a medium saucepan over low heat, combine the white chocolate chips, sweetened condensed milk, and unsalted butter. Stir continuously until the mixture is melted and smooth.
Remove the saucepan from the heat and stir in the vanilla extract and a pinch of salt for flavor enhancement.
Gently fold in the crushed Oreo cookies and rainbow sprinkles until they are evenly distributed throughout the fudge mixture.
Line an 8x8-inch baking dish with parchment paper, leaving some overhang for easy removal. Pour the fudge mixture into the prepared dish, spreading it evenly with a spatula.
Sprinkle additional rainbow sprinkles and crushed Oreos on top for decoration.
Cover the dish with plastic wrap and refrigerate for 2-3 hours or until the fudge is set.
Once set, lift the fudge out of the dish using the parchment paper, and cut into bite-sized squares.
Notes
Arrange the fudge squares on a colorful platter, and serve with additional sprinkles and whole Oreo cookies as a playful garnish.