When I was in Japan last year I saw the flower buds of Petasites (aka butterbur) being sold as a seasonal vegetable in a small market in Yunishigawa. Of course I screamed out loud (as is my wont), and it was much to Cayce's credit that she neither fled nor visibly cringed with embarrassment. I hadn't realized it was edible. That evening we were served butterbur tempura, and later in the week we ate the stems of the plant as pickles and in stews.
In the U.S., rumors of toxins keep many people from eating butterbur (and sassafras and hay scented fern and who knows what else), although it's frequently listed as an herbal remedy for migraines. The fear of inadvertent poisoning may be why I was unable to dig up any recipes (in English!) for butterbur flowers, other than the traditional tempura. Nonetheless, it's my first found edible plant this season and I'm thrilled to see it raise its flowery head.
If anyone out there has a recipe for the flowers, please let me know. Otherwise, I'll wait till the flower stems (aka scapes) lengthen, then use them in stir fry or maybe pickle them. And of course, I'll continue to research any and all possibilities. I think the leaf stems (not the leaves themselves) may also be edible, as with rhubarb.
Petasites flowers before the leaves emerge; in my garden the buds push up through last fall's leaves before I've had a chance to rake them off the beds. The scapes lengthen to about 8-10 inches as the buds open. Next, large (and I mean LARGE) leaves unfurl.
Petasites can be invasive, but the leaves are highly ornamental and when you need something to cover a lot of ground (shady, moist ground) it's very useful.
And hey, if it gets out of hand you can always eat it!