In a large saucepan melt butter over low heat. Add marshmallows and stir until completely melted. Remove from heat.
Add Rice Krispies. Stir until well coated.
Evenly press mixture into 13 x 9 x 2 inch pan, coated with cooking spray.
Cool. Cut into 2 inch squares.
In a small saucepan combine carmels, condensed milk and butter. Cook and stir over low heat until smooth.
Spread about 1 teaspoon of the caramel mixture over each bar. Top with apple slices. Spread remaining caramel mixture over cut edges of apple slices.
In small microwave-safe bowl combine chocolate chips and shortening. Microwave on high for 30 seconds to 1 ½ minutes or until smooth, stirring every 30 seconds. Drizzle over caramel.
Refrigerate about 15 minutes or until chocolate is set.