Adapted from Candy Recipes & Other Confections by May B. Van Arsdale and Ruth Parrish Casa Emellos.
Ingredients
The base of the candy:
1 cup (2 sticks) unsalted butter
1 cup sugar
1 hefty pinch of salt
1 T light corn syrup*
First Optional Topping
6 oz semi sweet chocolate, chopped (John's family used chocolate chips; I used plain chocolate)
Approx. 1 cup chopped pecans (I used a tad more)
Second Optional Topping
6 oz good quality milk chocolate, chopped
Approx. 1 cup chopped roasted, salted peanuts (I used a tad more)
Several pinches (to taste) of good quality, coarse sea salt
Instructions
Prepare a cookie sheet by lining it with foil (not strictly necessary, but I prefer to line my cookie sheets). Make sure your cookie sheet has a rim. Spray the foil with nonstick spray and then wipe with a paper towel, so that the layer of grease is not thick. The recipe calls for buttering the sheet, but I had problems with the butter melting and pooling; this seemed to work better for me.
In a 2-3 quart heavy stainless steel or copper sauce pan melt 2 sticks of butter at a very low temperature. When the butter is melted, add the sugar and salt, stirring all the while. As the butter and sugar blend, gradually increase the heat to medium, stirring most of the time with a wooden spoon. When the mixture is blended, add the light corn syrup. Continue to cook with the candy thermometer in the pan until the mixture reaches 300 degrees. Stir it often, especially at the end, so that it does not burn.
Working quickly, pour the mixture out onto the prepared cookie sheet. It will spread out and cover the pan in a fairly thin layer (mine covered about ⅔ of the pan and was thicker than John remembered--I have no idea why). Wait a few moments, maybe 1-2 minutes, then sprinkle the chocolate over the top of the toffee, spreading it out as it melts. Then sprinkle your topping of choice over the chocolate, pressing quickly and lightly to encourage the nuts and salt (if using) to stick. Chill until hard and cold. Break into edible pieces and store in cookie tin or other container. Store in the refrigerator or in a cool spot in the house (mine has been fine on the dining room table, but the original recipe did call for chilling).
*Note from John's mom: "The [light corn] syrup was not in the original recipe. Years after my mother was making this candy, we learned that by adding the syrup, we were able to ensure that the mixture of butter and sugar would become more stable. This lessened the chance that the two ingredients would separate and we would have to start it all over from scratch."
Recipe by The Spiced Life at https://www.thespicedlife.com/family-recipes-butter-crunch-2-ways/