Some type of Stachys like S. monieri or officinalis.

One of the white flowered cultivars of Stachys monieri or perhaps officinalis.

There seems to be confusion between those two sp. I see both S. 'Rosea' and 'Hummelo' that I have listed as either. Reliable sources such as Missouri Botanical Garden. list both as S. officionalis.

According to Encyclopedia of Perennials (2006, Dorling Kindersley, London) when compared to S. officinalis the S. monieri is a rarely seen, noticeably shorter-growing plant with longer flowers. And 'Hummelo' and 'Rosea' are both cultivars of S. officinalis.