Line a 13-in. x 9-in. pan with foil; butter the foil with 2 teaspoons butter and set aside.
In a small saucepan, combine the milk chocolate chips, butterscotch chips and peanut butter; stir over low heat until melted and smooth. Spread into prepared pan. Refrigerate until set.
For filling, in a small heavy saucepan, melt butter over medium heat. Add sugar and milk; bring to a gentle boil. Reduce heat to medium-low; cook and stir for 5 minutes. Remove from the heat; stir in the marshmallow creme, peanut butter and vanilla until smooth. Add peanuts. Spread over first layer. Refrigerate until set.
For caramel layer, in a small heavy saucepan, combine the caramels and cream; stir over low heat until melted and smooth. Cook and stir 4 minutes longer. Spread over filling. Refrigerate until set.
For icing, in another saucepan, combine chips and peanut butter; stir over low heat until melted and smooth. Pour over the caramel layer. Refrigerate for at least 4 hours or overnight.
Remove from the refrigerator 20 minutes before cutting. Remove from pan and cut into 1-in. squares. Store in an airtight container.
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