Preheat the oven to 350 degrees F.

Place the sesame sees on a large cookie sheet or jelly roll pan and toast them in the oven for 15 minutes.

Place the seeds in a 3 quart pan. Add the sugar, corn syrup, 1/3 cup water and margarine to the sesame seeds.

Bring to a boil over medium heat, stirring constantly.

Once it's come to the boil, continue to cook without stirring until the temperature reaches 270 degrees F on a candy thermometer or until a small amount of the mixture forms a ball when dropped into very cold water. (I don't have a candy thermometer, so I use the ball test.) This can take 15 to 20 minutes or more. The ball should be "plastic" in texture but should hold the ball shape.

Grease a jelly roll pan.

Stir the baking soda into the sesame seed mixture and pour into the jelly roll pan.

Spread the mixture with a metal spatula so it is 1/4 inch thick.

Cool completely and then break into pieces.

Don't forget to brush your teeth well after munching on these.