The magic number you are waiting for is 300°F, the hard crack stage. This can take 10-15 minutes. As it passes 250°F (hard ball), the color will deepen to a beautiful amber. Do not walk away. When the thermometer reads a steady 300°F, immediately remove the pot from the heat. Working quickly but carefully, stir in the vanilla extract. It will sizzle and steam dramatically—that’s normal. Immediately pour the hot toffee onto your prepared baking sheet. Tilt the pan to help it spread, or use your spatula to guide it into a thin, even layer. It sets incredibly fast, so you have to move with purpose.
While the toffee is still piping hot, immediately sprinkle the chocolate chips evenly over the top. Let them sit for 1-2 minutes; the residual heat will melt them perfectly. Then, use your offset spatula or the back of a spoon to gently spread the melted chocolate into a smooth, even layer over the entire surface of the toffee. Now, sprinkle the finely chopped toasted nuts over the wet chocolate, pressing them in lightly so they adhere. Finish with a delicate sprinkling of flaky sea salt. Let the toffee cool completely at room temperature until the chocolate is set. Do not refrigerate to speed this up, as it can cause the chocolate to bloom (develop white streaks). The wait is agonizing but worth it.
Pro Tips for Best Results
I tested this recipe three different ways: with a thermometer, using the cold water test, and going by color/foam alone. The candy thermometer is the only guaranteed path to success for a beginner. The cold water test is tricky, and judging by color alone led me to undercook one batch (sticky and chewy) and nearly burn another. A digital thermometer removes all guesswork.
Here’s what I learned the hard way about the nuts: if you sprinkle room-temperature or cold nuts onto the hot toffee before the chocolate, they can cause the toffee to crack and contract in spots. Adding them on top of the melted chocolate is the perfect insulator. The chocolate acts as a glue, and the nuts stay crunchy without affecting the toffee’s structure.(See the next page below to continue…)