Actually I have two favorites. Chocolate of course and Butterscotch. My mother used to go insane when people would refer to it as "Peanut Brittle." She really was famous for it.
It has only two ingredients, butter and light brown sugar (you can get away with one stick of butter and one of margarine). However, it is very difficult to make. You start with two sticks of butter (or one of margarine) and a box of light brown sugar poured over the butter in a cast iron frying pan. Prior to that you lay walnut pieces on cookie sheets. You turn on the heat and start stirring and don't stop. When the ingredients combine and turn a certain shade of light brown and start bubbling, you remove it immediately and pour the candy in streams over the walnuts on the cookie sheet. You only have seconds to pour the candy so the sheets better be right there. It then hardens and when it cools you break it apart willy-nilly.
Here's the rub. There's no "candy thermometer" involved simply because you don't have time to use one. You literally have seconds to realize it's done (even she used to make batches she had to throw out). Literally, a few seconds too soon and it's too granular. A few seconds too late and it's burnt. She was famous for it, but although everyone I know has tried it, none have yet to succeed. If you have about forty bucks to throw away, go ahead and try. If you succeed, the results are spectacular.