Line a 9×13 pan with parchment paper, lightly mist with nonstick cooking spray, and set aside.
In a large pot, melt the butter until it just starts to brown, giving it a nutty aroma.
Stir in vanilla extract, then add salt and marshmallows. Stir until fully melted.
Add Rice Krispies in 2-cup increments, stirring until combined.
Mix in M&Ms and holiday sprinkles. Pour the mixture into the prepared pan and gently press it to the edges.
For the garnish, melt white chocolate and drizzle half onto the treats. Sprinkle M&Ms and sprinkles, then drizzle the remaining white chocolate to secure the toppings.
Allow the white chocolate to set for a festive, delicious holiday treat!