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, or they'll be 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.
Melt the chocolate chips and shortening in the microwave in 20 intervals, stirring after each interval, until the chocolate is completely melted. Pour into a wide, tall glass. This will help when dipping.
Take the Krispie Treats and dip them into the melted chocolate about halfway. Place on a parchment-lined baking sheet. Allow the chocolate to set. Enjoy!