Scutellaria orientalis

Yellow flowered skull cap or helmet flower. A rhizomatous, woody based, low growing perennial, which flowers boldly and then occasionally from late sprung on. It is incredibly hardy coming from the tundra. 10-30cm tall.  Soft grey-green foliage which cascades beautifully.  Haircut to maintain the form you want.

I forgot to photograph in full bloom. What a sight!