01 -
Line a 9-inch square baking dish with parchment paper and set it aside.
02 -
In a large saucepan over medium heat, melt the butter. Add all but 1 cup of the marshmallows and reduce heat to low, stirring until completely melted.
03 -
Remove the saucepan from heat and stir in vanilla extract. Add cereal and the remaining 1 cup of marshmallows, stirring gently until combined. Fold in 1 cup of the M&M's and all the sprinkles.
04 -
Pour the mixture into the prepared baking dish. Press gently with fingertips until evenly spread.
05 -
Drizzle the top with melted white chocolate and add the remaining ¼ cup of M&M's and extra sprinkles if desired. Allow to set for 1 hour before cutting and serving.