Butter a 2 quart glass or metal bowl and set aside. Place all ingredients, except chocolate chips and nuts, into a heavy 3 quart sauce pan. Cook over medium heat, stirring constantly (without scraping sides of pan) until mixture comes to a full rolling boil. Place a candy thermometer into the boiling mixture and continue boiling, stirring occasionally, until temperature reaches 290 degrees F.
Remove from heat and pour into prepared bowl. Do not scrape sides or bottom of pan. Allow toffee to cool for approximately 30 minutes. After mixture has cooled, turn out of bowl, upside down, onto a wooden or plastic cutting board.
Heat chocolate chips in microwave for approximately 30 seconds, just until melted. Stir in nuts and pour chocolate mixture over the top of the toffee. Chill just until chocolate mixture hardens.