Adapted from the illustrious David Lebovitz
(who offers some good tips and encouraging words regarding candy making in the previous link).
Panela is a cone-shaped sugar available at Latin-American groceries. If you can't find it, you can substitute muscovado or dark brown sugar.
Use any nut you like as well; pecans, cashews and brazil nuts would both be lovely.
Sugar likes to crystallize, which is what you don't want when making toffee. To minimize the chances of this happening, agitate the sugar mixture as little as possible while it's cooking and when spreading it over the nuts. Have a clean pastry brush and a cup of water handy to brush down the sides of the pot if any crystals start to form. All that being said, fear not: during the countless times I've caramelized sugar, I've only had it crystallize a couple of times. If your mixture does crystallize, you can try adding a few tablespoons of water to the pot, give it a stir (it will bubble vigorously - careful!) and return it to the heat. It may re-dissolve and be saved.
Nutritional values are based on one of twelve servings.