Microwave butter in a large microwaveable bowl on high for 45 seconds or until melted. Add marshmallows and toss to coat. Microwave for 45 seconds and stir. Microwave for another 45 seconds or until marshmallows are completely melted and stir until well combined. Add the cereal and mix well. Press mixture into a foil-lined 13" x 9" pan sprayed with cooking spray. Tip: Spray the back of a spoon or spatula with cooking spray to help press the cereal without sticking.
Microwave the caramels and milk in a medium microwaveable bowl for 2 to 2 1/2 minutes or until caramels are completely melted, stirring after each minute. Pour caramel over cereal and spread evenly. Sprinkle with chopped pecans and press lightly into the caramel to secure.
Microwave the chocolate in a small microwaveable bowl for 1 minute or until completely melted, stirring every 30 seconds. Drizzle chocolate over the nuts and caramel. Allow treats to cool and set before cutting to serve. Tip: To quickly cool the treats, place them in the refrigerator or freezer for 10-20 minutes before cutting.