Line a 9×13 baking pan with parchment paper. Lightly grease the parchment and pan with nonstick spray. Set aside.
Add the butter to a large pot over medium low heat. Let it melt completely. 1/2 cup unsalted butter
Add in 6 cups of the marshmallows, and stir together gently until marshmallows are completely melted. 7 cups mini marshmallows
Remove the pan from the heat and stir in the vanilla extract and salt. 1 tsp vanilla extract, 1/4 tsp salt
Add in the cereal, and remaining 1 cups of marshmallows and stir until the cereal is coated evenly with the melted marshmallow mixture, and the other marshmallows just start to melt. 8 cups crisp rice cereal
Scoop half of the mixture into the prepared pan.
Sprinkle 1/3 to 1/2 of the mini m&ms over the top of the rice krispie treats. 1 cup mini Christmas m&ms,
Transfer remaining rice crispy treats into the prepared pan.
Using a greased rubber spatula gently press the mixture down into the pan. Do not press them hard.
Sprinkle with remaining m&ms, and holiday sprinkles. 2 TBS Christmas sprinkles
Allow the treats to cool to room temperature for about 1 hour.
Add the white chocolate chips to a small bowl and microwave in 20 second increments, stirring after each until you can stir it smooth. 1/2 cup white chocolate chips
Transfer the white chocolate to a ziptop bag and snip the corner. Drizzle over the top of the treats. Let white chocolate sit until set.