Melt butter in a large, deep sauce pot (5 quarts) over low heat.
Once butter is mostly melted, add marshmallows and stir until smooth (this takes about 3-6 minutes).
Once butter/marshmallow mixture is smooth remove the pan from the heat, add vanilla extract and stir to combine.
Add crispy rice cereal and sea salt to the large pot with the marshmallow mixture and mix until combined. (If desired, at this point you can add mix-ins like sprinkles M&Ms, etc.)
Quickly pour the rice crispy treat mixture into the prepared pan.
Use a greased spatula or greased hands to gently press the rice crispy treat mixture into the pan until the top is level.
If desired, at this point you can add sprinkles, chocolate chips, etc. to the top. Just be sure to gently press them onto the top of the rice crispy treats.
Allow the rice crispy treats to sit at room temperature until cooled, about 1 hour.
Cut into 9 or 16 squares and serve!
Video
Notes
Ingredient Substitutions
Crispy rice cereal. Generic or name brand cereals both work very well in this recipe. I have also used brown rice crispy cereal with great results! You could have fun and substitute some (or all) of the crispy rice cereal with another cereal like fruity pebbles, cocoa pebbles, etc.
Mini Marshmallows. Large marshmallows don't melt as well as minis, but one 10 oz bag of mini marshmallows equals 40 regular marshmallows (or you could weigh the larger marshmallows and use 10 oz or 283 g).
Salted Butter. unsalted butter works well. Or, try using brown butter, it's delicious.
Sea Salt. If using iodized salt I recommend decreasing the amount by half.
Vanilla extract. Vanilla bean paste can be used in place of extract.
StoreStore leftovers by wrapping them in plastic wrap and putting them in an airtight container or ziplock bag at room temperature - do not refrigerate.FreezeLet them cool completely, then wrap them in plastic wrap and put them in an airtight container or ziplock bag in the freezer for up to 1 month. Set them out at room temperature for 1 hour before serving.