Sorry if I am repeating myself here (have not re-read the whole thread) but I am rather pleased with my scorzonera patch, 3 years old by now. I dug one up the other day and it had expanded into a number of separate thongs, very long, fairly slim, and also hollow, which worried me.
Cleaned them, boiled them in water and vinegar, peeled them (black skin rubs off fairly easily), and added them to a chicken casserole to bulk it out. They were tender in spite of being hollow, and tasted really quite interesting.
I won't be eating them every day, but they have earned their space as perennials. You can never get the whole root out, and I have found, where I think I have dug it out, that eventually they reappear like dandelions. But much nicer. You can eat the smaller fresh leaves in spring without apparently damaging the plant.
I need to get them into an out-of-the-way corner, like horseradish, and just let them do their own thing until I feel like digging some.
Anyone else growing them?