Before starting your Rice Krispie treats, generously butter a 9"x9" or 8"x8" baking pan. On a flat cutting surface, cut 2 cups of large marshmallows into quarters. Set aside.
In a large pot, over medium-low heat, add unsalted butter and 6 cups of marshmallows (minus 3 marshmallows). Stir occasionally until butter and marshmallows have melted. Remove from the heat.
Add vanilla extract and salt. Stir to combine. Add 7 cups of puffed rice cereal, stir until marshmallow mixture is covering all rice cereal. Add cut marshmallows into Rice Krispie treat mixture, mixing one final time.
Poor your gooey Rice Krispie mixture into the prepared baking pan. Cover the surface with plastic wrap and use your hand to pack down the Rice Krispie mixture into the pan (note: the plastic wrap prevents the marshmallow mixture from sticking to your hands during the flattening). Allow to cool.
Use a rubber spatula to help invert the Rice Krispie treats onto a cutting board.
In a microwave safe bowl, melt your chocolate chips (note: I recommend heating chocolate chips in 30s increments, stirring until 2/3 of chocolate is melted. Then, stir the mixture one final time to finish the melting process).
Spread a thin layer of melted chocolate onto the Rice Krispie treats. Add your halloween sprinkles. Let cool for approximately 10min in the fridge, until the chocolate has hardened.
In another microwave safe bowl, heat 3 marshmallows for 30s on high. Stir. Wearing disposable gloves, add some melted marshmallow into your hands and spread your hands apart, creating large webs of marshmallow that can be draped over your Rice Krispie treats. Continue until Rice Krispie treats are covered in marshmallow webs. With buttery hands, press down any marshmallow webs that are not adhered to the Rice Krispie treats.
Using a buttered knife, cut into squares, serve, and enjoy!