Stylophorum diphyllum 

Celeandine Poppy, Wood Poppy. Lovely bright yellow, easy in woodland or sunny position. 40cm x 40cm  Hardy and easy, great to have.  Woodland or eve a shady border, under shrubs.  I have found another version of this plant, (naming is tricky) the other version is often seen online, it has greener leaves which are much larger. This is more blue green and even paler on the reverse and a smaller more compact plant.  The two toned effect is pretty as the leaves tend to grow quite upright (another variation) so that especially in the dew, it is a sparkling  clump.