Cover the bottom of a 9 by 9 pan or small cookie sheet with aluminum foil that has been sprayed with cooking spray. (To use a cookie sheet double the recipe.)
Combine the butter, sugar, and salt in a heavy saucepan.
Bring to a boil over medium heat…stirring often. Bring it to a gentle boil.
Cook until it darkens in color about 10-20 minutes. (technically that is 285 degrees)
If you drop some of the mixture into ice water, wait a bit for it to cool, and it stays hard when you take it out of the water...it's done.
When the toffee reaches the hard crack stage pour it into the sprayed pan.
Immediately sprinkle the top with the chocolate chips. Leave for a minute to soften and the spread gently.
Sprinkle the nuts on top and gently press in.
Pop into the fridge until set.