1. Combine butter, sugar, and salt in a large, heavy-bottomed saucepan over medium heat; stir constantly in one direction until butter is melted, about 5 minutes.

2. Meanwhile, line a 9x13-inch baking dish with a sheet of parchment paper, letting it overhang two sides of the dish.

3. Once the butter has melted, stop stirring and bring mixture to a boil. Once boiling, cook, stirring only 2 to 3 times, until it turns a dark amber color and the temperature reaches 285 degrees F (137 degrees C) on a candy thermometer, 20 to 30 minutes.

4. Immediately pour toffee into the prepared baking dish. Sprinkle chocolate chips on top and let sit until they soften, 1 to 2 minutes. Use a spatula to spread softened chocolate into a thin, even layer. Sprinkle nuts over the chocolate and press down slightly; wearing a plastic bag over your hand will minimize the mess.

5. Place toffee in the refrigerator until set, about 1 hour.

6. Lift hardened toffee out of the baking dish with the parchment paper. Break into pieces and store in an airtight container.

Tips

Use chopped walnuts or pecans instead of almonds if preferred.