When this blooms we sound like that shampoo commercial 'Yes! Yes! Oh Yes!"  Perfect quarter-sized mega-double white flowers like a steroidal double Anemonella, this has attained Enlightenment in the realm of Buttercups.  Non-running tidy clumper & a sterile non-seeder.  Easy.

A seldom encountered Buttercup from the Pyrenees.  This is so well mannered that one has a tendency to think of it as a Trollius rather than a Ranunculus. Thick short rhizomes create a dense crown with rich green leaves and deep yellow flowers of good substance. Nice.