SPRAY large bowl with nonstick cooking spray.
HEAT, marshmallows and butter in large, heavy-duty 6-quart saucepan over medium-low heat, stirring frequently, for 5 to 10 minutes, until smooth. Remove from heat.
WORKING QUICKLY, stir in cereal. Carefully transfer mixture to prepared bowl. Cool for 5 minutes.
LINE baking sheet with wax paper. Spray 24 mini muffin cups and hands with nonstick cooking spray.
PRESS about 1/3 cup marshmallow mixture into prepared muffin cups, shaping mixture above cups into rounded “ice cream scoop” shapes with ice cream scoop or two tablespoons.
MICROWAVE 1 1/4 cups morsels and vegetable shortening in dry, uncovered, microwave-safe bowl on HIGH power for 45 seconds; STIR. The morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until morsels are melted.
DIP tops of sundaes in chocolate. Immediately decorate with sprinkles and remaining 1/4 cup morsels. Let stand until chocolate is firm. Store in airtight containers. Before serving, top each “sundae” with 1 tablespoon whipped topping and a cherry.