In heavy 1-quart saucepan, heat 1/3 cup sugar over medium heat until sugar begins to melt. Stir until sugar is completely dissolved and caramel colored. Cool slightly until caramel has thickened slightly. Drizzle hot caramel over bars. (If caramel begins to harden, return to medium heat and stir until thin enough to drizzle.) After caramel on bars has hardened, cover and refrigerate bars up to 48 hours.