In a heavy saucepan, combine the sugar, corn syrup and vinegar. Cook over medium heat, stirring constantly, until sugar dissolves. Cook without stirring until the temperature reaches 300° . on a candy thermometer. Do not overcook.
Remove from the heat and quickly whisk in baking soda (it will start to foam up, but quickly whisk in until you can’t see baking soda anymore).
Pour onto a lightly greased parchment paper lined jelly roll pan. It will be large and foamy but will fall as it cools. Do not press or spread the candy.
When mixture is cool, break into bite-sized pieces.
OPTIONAL: Dip into melted chocolate; place on waxed paper until the chocolate is firm. Store candy in an airtight container.
Sponge candy is a crunchy, airy candy with a light sweet flavor. It is a delicious candy, perfect to give as gifts.