Grease a 9x13 pan with butter and set aside. Save butter wrapper for later.
In a large pot, melt butter, then add marshmallows and melt on medium-low until smooth.
Remove the mixture from the heat and stir in the vanilla extract, followed by the cereal. Mix until evenly coated.
Transfer the mixture to the buttered pan, level it with an offset spatula or gently pack them into the pan with the buttered side of the butter wrapper, and allow it to cool for 10 minutes while you melt the semi-sweet chocolate in a shallow bowl. Melt in 20-second increments in the microwave, stirring in between.
Butter the Mickey cookie cutter and prepare a sheet of waxed paper to transfer treats once they are cut.
Cut out treats and transfer them to the waxed paper.
Dip a popsicle stick in melted chocolate and then into a Mickey Treat.
Dip one side of the treat in chocolate.
Sprinkle with mini M&M’s and drizzle with additional chocolate if desired. (We used a piping bag. You could use a ziplock bag with a small hole cut out of the corner or drizzle with a fork.)
Allow to set in the refrigerator for 10 minutes or at room temperature.