A very pretty and easily grown little poppy with large, sulphur yellow flowers produced over a long period from late spring to late summer. It forms neat and tidy little clumps of greyish leaves. It is a poppy, so it will seed itself about if you allow it, but it is so dainty that it isn't a weedy nuisance. About 15cm (6") high.
Now listed as P. nudicaule, this used be considered a cultivar of Papaver miyabeanum (from Japan?) and that still seems more likely to me.