Marilyn's English Toffee

From Marilyn on America's Test Kitchen forum site, with a couple changes.

• Ready In: 40 mins
• Serves: 32
• Yields: 3 pounds

Ingredients

• 1  lb unsalted butter
• 1⁄2 teaspoon table salt
• 2  cups granulated sugar
• 3  tablespoons water
• 1  cup  slivered almonds (do not use sliced almonds)
• 12  ounces  semisweet chocolate (chips are fine)
• 2  cups pecans, lightly toasted and finely chopped

Directions

1. Line a large jelly roll or half-sheet pan with heavy-duty foil and butter the foil or just use a Silpat.
2. Melt the butter with the salt in a heavy 3 quart saucepan over medium heat. Slowly add the sugar, stirring constantly with a wooden spoon. Add the water about halfway through this process.
3. After all the sugar is added, begin testing the mixture to see if the sugar is dissolved. The mixture will probably be boiling at this point.
4. When sugar is dissolved, add the almonds, and increase the heat to medium high. Cook to the hard-crack stage, or about 310-320 degrees on a candy thermometer, stirring often to keep the candy from burning on the bottom. When it’s done, it should be a medium-dark amber color and have a caramel aroma. The almonds should have a toasted color but they should not burn. I use a temperature right in the middle, 315 degrees.
5. Remove from heat and pour into the prepared pan, spreading as evenly as possible with an offset spatula. Be careful, this stuff is hot! Sprinkle the chocolate chips all over the toffee, and wait a couple of minutes until they melt. Then spread the chocolate evenly over the toffee. Sprinkle with chopped nuts, and press them in gently with a spatula or bottom of a glass to anchor them in the chocolate.
6. Allow the toffee to harden at least 6-8 hours. Break into pieces. Store in an airtight container in a cool place.