You can also make this caramel brittle with other nuts, such as slivered almonds or pistachios.
- Vegetable oil, for pan and knife
- 4 cups sugar
- 1/4 teaspoon apple-cider vinegar
- 5 1/2 cups hazelnuts
Oil an 11-by-17-inch baking pan. Stir sugar, vinegar, and 1 cup water in a medium saucepan over medium heat until sugar dissolves. Cook without stirring until dark amber, 18 to 25 minutes. Stir in nuts.
Pour mixture onto pan. Let set until firm but still soft enough to cut. Unmold onto a cutting board. Working fast, use an oiled chef's knife to cut into six rectangles.