Mix cake mix, butter and egg in bowl. Press in the bottom of a 9 x 13 inch pan and bake at 350 degrees for 12 to 18 minutes. Remove from oven. Sprinkle with marshmallows. Return to oven for 1 to 2 minutes, or until the marshmallows begin to puff. In saucepan, heat corn syrup, 1/4 cup butter, vanilla, and chips until melted. Remove from heat and stir in Rice Krispies and peanuts. Spoon over marshmallows, spread to cover. Chill and cut bars.