Fill a large bowl with 6 cups of Rice Krispies cereal. Set aside.
Spray a 9x9 baking dish with nonstick spray. Set aside.
In a large pot add the unsalted butter and stir until melted.
Add the 10 ounce bag of marshmallows to the pot and continuously stir until they completely melt.
Add in the vanilla extract, salt, and sweetened condensed milk, stirring everything once again until combined.
Remove the marshmallow mixture from the heat and pour over the bowl filled with the Rice Krispies cereal. Use a large wooden spoon or rubber spatula to fold the ingredients together until evenly distributed.
While the mixture is still warm, add the mini marshmallows, christmas M&Ms, and half of the Christmas sprinkles. Fold the two together briefly so that the M&Ms don’t melt.
Transfer the mixture to the prepared baking dish and press into the pan evenly.
Let the treats sit at room temperature for about an hour before eating.
Cut and enjoy or store in a ziploc bag or a tightly sealed container for later. Enjoy!