We adapted this recipe from the Irish food authority Darina Allen's book The Complete Book of Irish Country Cooking (Penguin Studio, 1996).
- 2 tbsp. plus 1 tsp. butter
- 1 (16-oz.) bottle light corn syrup
- 1 1⁄4 cups light brown sugar
- 2 tsp. white vinegar
- 2 tsp. baking soda
Butter an 8 1⁄2" x 12" baking pan with 1 tsp. of the butter and set aside. Melt the remaining 2 tbsp. butter in a medium, deep saucepan over medium-high heat. Add corn syrup, sugar, vinegar, and 2 tbsp. water and stir until sugar dissolves, about 5 minutes. Continue cooking sugar mixture, without stirring, until temperature reaches 300º on a candy thermometer, 10–15 minutes.
Working quickly, remove saucepan from heat, carefully sift in baking soda, and vigorously whisk (hot syrup will bubble up in pan) until baking soda is completely incorporated, about 5 seconds. Immediately pour into prepared pan. Set aside until candy is hard and completely cool, about 30 minutes, then break into pieces with a hammer. Store in an airtight container for up to 4 weeks.