Here is what you'll need
1 cup sugar
1 cup dark corn syrup
1 tablespoon apple cider vinegar
1 tablespoon baking soda
Line an 8-inch square pan with buttered foil, allowing the sides to extend over the top. Butter the foil generously.
Add sugar, corn syrup, and apple cider vinegar in a large heavy-duty deep saucepan. Continuously whisk over medium heat until sugar dissipates. Continue cooking (but do not stir) take a clip-on candy thermometer and carefully attach to the side of your saucepan. 300 F is the target temperature (this is a hard-crack stage) gently swirl the pan occasionally (but do not stir), it takes about 15 minutes depending on the strength of your stovetop.
The following stages move swiftly so be prepared :) Carefully remove from heat and immediately add baking soda and whisk quickly until well combined (the mixture will get bubbly in a hurry).
Immediately pour mixture into your prepared foiled pan. Allow cooling (about an hour).
Remove candy by lifting foil and peel away edges. Break candy by whacking with a hammer or knife handle in large pieces.
Decorate with your favorite coating chocolates and enjoy :)