1. Beat the 1 cup butter or margarine and brown sugar until fluffy in a large bowl with electric mixer at medium speed; beat in egg and 1 teaspoon of the vanilla.
2. Turn mixer speed to low and blend in flour and salt. Spread evenly in a 15x10x 1-inch jelly roll pan with a spatula.
3. Bake in moderate oven (350°) 25 minutes, or until golden.
4. While cookie base bakes, combine butterscotch pieces, corn syrup, the 2 tablespoons butter or margarine and remaining 1 teaspoon vanilla in the top of a double boiler; heat, stirring several times, until butterspotch pieces melt and mixture is smooth; stir in peanuts and cereal.
5. Spread mixture over cookie; base. Bake 5 minutes longer, or until topping is set. Remove pan to wire rack and cool 15 minutes. Cut into 72 bars. Cool completely before removing. Store in metal tin.