Line a 8x8 or 9x9 with parchment paper. Lightly grease the parchment. I always use a very light mist of nonstick spray. Set aside.
Melt the butter over low heat in a large pot or Dutch oven. Once melted, add the 10-ounce bag of marshmallows. Stir the mixture until the marshmallows are just melted. Stir in the salt and vanilla to combine.
Remove the pan from the heat, add the Rice Krispies, and mix until coated with the marshmallow mixture.
Immediately stir in an additional one cup of marshmallows and a cup of mini chocolate chips. The chocolate chips will melt throughout perfectly.
Turn the mixture out into the prepared pan and, using a wooden spoon or spatula that has been coated in non-stick cooking spray, lightly press the mixture into an even layer. Do not pack it down with force.
Sprinkle the 2 tablespoons of mini chocolate chips on the top and lightly press them into the treats. This step will help them stay on top.
Allow treats to set for at least 1 hour at room temperature and up to 1 day. Cover tightly if leaving out for more than a few hours.
Lift the treats as a whole out of the pan using the edges of the parchment paper. Cut into squares.
Cover and store leftover treats at room temperature for up to 3 days. To store, place in an airtight container, with sheets of parchment or wax paper between layers.