Edelweiss Chocolates in Beverly Hills makes a delicious toffee, but when I want to make it at home, I turn to my aunt Tina's toffee recipe. Every holiday season my aunt Tina and my mom would make a giant batch, with aunt Tina in charge and my mom as a helper. Our house would be filled with sheet pans of cooling toffee, with aunts and friends chopping nuts and melting chocolate. It's the go-to Thomas family gift, and I can't imagine a Christmas without it.
Heat the butter, sugar, kosher salt and 1/4 cup water in a medium saucepan fitted with a candy thermometer over low heat, stirring with a wooden spoon. When the mixture starts to boil, turn the heat up to medium. Cook until the mixture reaches 302 degrees F, 15 to 20 minutes. Turn off the heat and add the vanilla, stirring to incorporate. Be careful not to burn yourself or the mixture.
Immediately pour the hot toffee into the 2 prepared baking sheets and smooth until evenly coated and 1/8 to 1/4 inch thick. Put the pans into the fridge to let the toffee cool (this will take several hours, or leave the toffee in overnight, uncovered).
Once the toffee has cooled, carefully loosen the pieces (you can do this by hand or with a knife). If it cracks, it's not a big deal.
Melt the chocolate over a double boiler, stirring to combine. Use a spatula to coat one side of the toffee with the chocolate, and then immediately top with a heavy sprinkle of the pecans and a sprinkling of flaked sea salt. This must be done immediately, because the cold toffee can cause the chocolate to harden before the pecans can stick. Put the toffee back in the fridge to cool the chocolate. Once it has hardened (it takes about an hour), flip and coat the other side with the chocolate, pecans and sea salt. You will probably have chocolate and pecans left over, which you can use for more toffee. Let the toffee cool in the fridge until hardened again.
When the toffee is ready, crack it into irregular pieces with your hands. Bag them or stick them in a tin for your own enjoyment.