Line a 9� x 13� baking pan with foil; generously grease the foil with butter and set the pan aside.
Measure out your baking soda and have it ready to go.
In a large (larger than you think you�ll need!) heavy saucepan, combine the brown sugar, corn syrup and vinegar over medium heat, stirring constantly, until the sugar is dissolved and the mixture comes to a boil.
Cook, without stirring, until a candy thermometer reads 300�F (hard-crack stage).
Remove from heat and add the baking soda, stirring rapidly. When you add the soda, the whole mixture will puff up�don�t be alarmed (this is where the �larger than you think you�ll need� saucepan comes in handy), and don�t stop stirring!
Once combined, immediately pour into the prepared pan. Do not spread the candy (it won�t fill the pan), and do not scrape the saucepan. Let the candy cool, undisturbed. Basically, keep your hands off as much as possible. Any stirring, bumping, shaking, smoothing, etc., will pop the air bubbles that make the candy so wonderful.
Once the candy is cool and set use the foil to lift it out of the pan. Gently peel back the foil and break the candy into pieces. Store in an airtight container (moisture will make the candy soften and collapse).
If you like, you can dip the candy in the chocolate coating of your choice�dark, milk, white or two-toned, it�s all delicious!