Sweet 'n' Salty Ice Cream Bowls

Melt butter in a large pot. Add marshmallows; cook, stirring, until melted. Off heat, stir in vanilla extract, cereal squares, broken pretzel sticks, and salted nuts. Spray 18 muffin-pan cups with cooking spray, then spray hands with cooking spray. Press mixture into muffin cups to form bowls (use handle of wooden spoon to press mixture into pans). Let sit 1 hour; remove from pans and fill with ice cream.