I was looking for a picture of herbs drying and found this:
Anthriscus sylvestris, known as cow parsley,[2] wild chervil,[2] wild beaked parsley, Queen Anne's lace or keck
https://en.wikipedia.org/wiki/Anthriscus_sylvestris
Have you tried smelling that plant?
This is probably not your plant though I have to ask, could that be parsley?
I have never seen parsley go to seed though I know parsley can have several different leaves based on variety.
I asked Google about parsley with white flowers and got the above link.