Butter an 8-inch x 8-inch pan, line with a parchment paper sling and set aside.
Melt butter and salt in a large saucepan over low heat. Add marshmallows and cook, stirring, until mostly melted. Remove from heat and mix in vanilla extract. Mix in rice crispy cereal. Add marshmallow cream and mix until well coated.
Scrape into prepared pan. Butter your hands and gently spread mixture into pan (don’t pack them down). Let cool at least 30 minutes. Remove from pan, cut into squares and enjoy.