Combine butter, mini marshmallows, and salt in a large pot over medium heat.

Heat the mixture while stirring constantly until marshmallows are melted and fully combined with butter.

Remove from heat and fold in Rice Krispies until full incorporated into marshmallows.

Press mixture into a rimmed sheet pan lined with parchment paper.

Let the Rice Krispy Treats sit and solidify for at least an hour before cutting into them.

Optional: cut treats out into shapes using cookie cutters and decorate with gel food coloring.