Preheat oven to 375°. In a processor, finely chop the nuts (work in batches) & transfer to a 12x16" pan. Drizzle the melted butter over the top, sprinkle very lightly with salt & toss. Bake for 8-10 minutes, stirring twice. Set aside to cool.
Meanwhile, unwrap all the candy bars & set aside. When the nuts have cooled, transfer half to a bowl & set aside. Spread the remaining nuts evenly on the baking sheet & top with 13 of the chocolate bars, breaking them up if you want to.
In a deep, heavy 3 qt pan, melt the 1 lb butter over low heat. Gradually whisk in the sugar. If the butter doesn't integrate into the sugar, use an electric hand mixer; it should be a thick creamy mass. Turn up the heat to medium low. Stir constantly with a wooden spoon at this point. Insert the candy thermometer. The mixture begins to darken immediately, marbling even. Don't leave it! Wipe down the sides of the pan 2 times with a dampened paper towel wrapped around a knife, or a pastry brush dipped in water - this keeps the sugar crystals on the sides of the pan from turning the candy back again to sugar.
When the candy thermometer reaches 250° stop stirring; the candy is nearly ready to pour. Then the mixture reaches 300° (this took about 13 minutes on my stove), pour immediately over the prepared nuts & chocolate. Top the hot toffee with the remaining chocolate bars, using a small rubber spatula to smooth the chocolate once melted. Top with the reserved nuts & with the back of a metal spatula, pat the nuts into the melted chocolate. Set aside to cool.
The chocolate needs to be firm before breaking into pieces, so place the tray in the refrigerator for 30-60 minutes. when the chocolate is firm, loosen the toffee patty with the tip of a knife & break into large chunks, then into smaller pieces with a cleaver. I made rough pieces, about 1-1 1/2" in size. (I should warn you the nuts scatter a bit around the kitchen.) Store the crumbs in the refrigerator, and the candytoo, or freeze both until needed. Bring almost to room temperature before serving.~~