Spray nonstick cooking spray on 2 cookie sheets. Wipe cookie sheets with a paper towel to coat entirely. 

Combine butter and sugar in a pan over medium-high heat. Bring to a rolling boil and stir in salt and vanilla.

Stir mixture constantly with a metal whisk, approximately 10 minutes, and bring candy mixture to hard-crack stage. (This is defined as between 300-320 degrees F on a candy thermometer. The thermometer should not be touching the bottom of the pan, as this can give a false reading.) Candy mixture should be a light-brown color. Watch very closely, as it can burn easily.

Perform the cold water test: Dip a metal spoon into the candy mixture, and then dip the spoon into cold or room-temperature water. Candy on the spoon should crack when pinched; it should not be a hard ball.

Work quickly to drizzle mixture in one long, thin strip down the middle of each prepared cookie sheet.  

Spread very quickly and as thin as you can with a metal spatula. The spread mixture should cover most of the cookie sheet.

Sprinkle chocolate chips on top of toffee and let melt for a couple of minutes. Then, spread chocolate with a metal knife, like frosting, to cover all of the toffee. 

Top with nuts, and tap down into the chocolate with metal spatula.

Let set overnight, if possible, or approximately 6-7 hours. Break into random pieces.