Preheat oven to 350 degrees. In a large bowl combine cake mix, butter, and egg. Beat at low speed until crumbly. Press into the bottom of an ungreased 13x9-inch pan. Bake for 12–18 minutes or until golden brown. Remove from oven and sprinkle with marshmallows. Return to oven and bake an additional 1–2 minutes or until golden brown.
Combine corn syrup, butter, and vanilla in a large saucepan; heat until chips are melted and mixture is smooth. Remove from heat, stir in cereal and peanuts. Immediately spread warm topping over marshmallows. Refrigerate 1 hour or until firm.