1. Preheat oven to 350 degrees Fahrenheit.
2. Beat margarine with sugar and vanilla extract. Add flour and salt, mixing well. Stir in chocolate chips.
3. Press into ungreased 10- by 15-inch baking pan. Bake for 20 to 25 minutes or until lightly browned. Cool for five minutes.
4. If desired, melt dark and white chocolate chips separately. Drizzle bars with melted chocolate.
5. Cut into bars while still warm.