My husband came across this recipe and we tailored it a bit to our liking. We've made it several times. It doesn't seem to last very long. We've tried a few different chocolates. It seems self explanatory, but spend a few extra dollars for the good chocolate. It really does make a difference.
1 pound unsalted butter
1 cup white sugar
1 cup brown sugar
1 Tbsp. corn syrup
1 1/2 to 2 cups raw pecans, chopped finely or ground loosely
2 tsp. vanilla extract or 1 vanilla bean (scraped or split so the seeds will come out inside the toffee)
1 tsp. salt
2 cups chocolate chips or shaved chocolate
Spread chocolate on a large silpat sheet, greased cookie sheet, or greased marble slab.
Melt butter in a heavy-bottomed pot on stove top. In separate bowl, mix together white sugar, brown sugar and corn syrup, add to melted butter. Add 1/4 cup water. Cook mixture on medium-high heat, stirring with a wooden spoon. Using a candy thermometer—most can clip onto the pot—cook until 260°, stirring hard and fast to make sure nothing is sticking to the pan and your toffee doesn't burn. At 260°, add the almonds, then lower the heat and finish cooking until your candy thermometer reads 300° and reaches the soft ball stage. It should take about 15 to 20 minutes total to reach the 300° mark. The mixture should be a beautiful, bubbly, golden brown color. At 300°, turn off heat immediately.
Add vanilla (if adding vanilla beans, you must fish them out when you pour the toffee before it cools) and add the salt. Stir quickly.
Pour the mixture out over the top of the chocolate. Smooth out the toffee to 1/4-inch thickness. After about 5 to 10 minutes, you can score the toffee with a knife or pizza cutter in order to break it up later. Using hot water and wiping the knife clean after every slice can help in scoring the toffee.
You may now let the mixture cool. When cool, you can sprinkle with a dash of fleur de sel (French sea salt), break them up and wrap them in cellophane or an airtight container to maintain the freshness.