Melt butter in a pot over medium heat (you can do this in the microwave too). Add marshmallows and heat until melted, stirring frequently.
Press cereal / marshmallow mixture into a greased 9"x13" pan.
Melt candy melts in microwave or double boiler according to package instructions. Pour into a plastic squeeze bottle and drizzle across bars.
Let cool for 1 hour and cut into squares.
Makes 12-16 servings, depending upon how big you made them. Store in an air-tight container for 1-2 days.