Line a baking pan with aluminum foil and grease the foil with butter.

Place the corn syrup, sugar and vinegar into a heavy-bottomed saucepan and cook the mixture over medium heat, stirring until the sugar is dissolved, and bring it to a boil.

Once the mixture is boiling, stop stirring it. Let it cook until it reaches 300°F.

Take the pan off the heat and get ready for the fun part. Dump in the baking soda and stir. The mixture will foam up like a special effect from a bad science fiction movie; it's supposed to do that! Just stir enough to incorporate the baking soda; if you mix it too much, you'll mix out all the air bubbles.

Pour the mixture into your prepared pan and tilt the pan to help the mixture spread out. Let it cool completely. Then you can use the foil to lift the candy out. Break it up into pieces. Pro tip: save the little sponge candy shards for things like ice cream topping.