Prepare a 9×13-inch pan by spraying it with butter cooking spray. Set aside.
In a large pot over medium heat, melt the butter and add salt. Use a rubber spatula to spread the butter up the sides to prevent the mixture from sticking.
Add the sweetened condensed milk to the melted butter and stir until well combined.
Add the 12 ounces of mini marshmallows. Stir over medium heat until the mixture is completely melted. Then remove from the heat.
Add the vanilla extract and stir until well combined.
Add the 7 cups of Rice Krispies cereal. Use the rubber spatula to stir it all together.
Pour the mixture into the prepared 9×13-inch pan. Wet your hands, shake off the excess water, and use your hands to gently press the Rice Krispies into the pan. Don't press them down too hard, as doing so makes your Rice Krispies hard to bite into! Let the treats cool at room temperature for an hour.
Using the rubber spatula, remove the treats from the pan. Use a knife to cut them into squares.
Take half of the Krispies Treats and top them with the Christmas sprinkles.
Melt the chocolate chips and the shortening in the microwave in 20 intervals until the chocolate is completely melted.
Take the remaining Krispie Treats and dip them into the melted chocolate, then top with Christmas sprinkles. Allow the chocolate to set. Enjoy!