In a large saucepan, combine butter, sugar, and salt. Cook over medium heat, stirring constantly until the mixture is melted together, which will take about 5 minutes.
Line a 9x13 baking dish with parchment paper. Make it large enough that it covers the ends of the dish for easy removal.
After the butter has melted and everything is combined, allow the mixture to come to a boil.
Cook the mixture, stirring 2 to 3 times while it cooks. You will know it's ready when it turns a dark amber color. Using a candy thermometer, see that it reaches 285 degrees F. This should take 20-25 minutes.
Pour the butter toffee mixture into the baking dish. Sprinkle the chocolate chips on top. Allow them to soften and then spread them into a chocolate layer with a rubber spatula.
Sprinkle the chopped nuts on top and place the dish in the refrigerator. It will take 1-2 hours for the toffee to cure and harden.
Once hardened, lift the toffee out of the dish and break it into serving sizes. Enjoy!