Line a 9x13-inch baking dish with foil and lightly grease it.

In a large pot over medium heat, melt the butter. Stir in the salt and vanilla.

Add the marshmallows and stir until melted and smooth, about 5 to 7 minutes.

Remove from heat and fold in the Rice Krispies cereal until fully coated.

Transfer the mixture to the prepared pan and let cool for 2 minutes.

With greased hands or rubber spatula, gently press into an even layer.

Let sit at room temperature for about 30 minutes, until firm.

Remove from the pan and place on a cutting board.

Melt the white chocolate in the microwave in 30-second intervals, stirring between each until smooth. Drizzle over the top, then add sprinkles and M&Ms.

Add another drizzle of white chocolate and a few more sprinkles for extra color.

Let set until hardened, then cut into squares and serve.