Cook nettle lightly in slightly salted water for a few minutes. Sauté chopped onion in a saucepan with olive oil. Add rice and toast a few seconds. Gradually add water leftover from nettle leaves to cook rice until done. (If more water is needed to finish cooking, use hot broth prepared with a small piece of bouillon cube). Soften with butter and grated Piave Extra Aged and serve very hot.