The upper surface is mostly black but with a white rim:
The lower surface is all white and shows about 4 pores per millimetre:
Under the microscope (x600, image width 86um) the spores are about 4.5 x 1.5um:
This is at the lower end of the size range of 4.5-6.5 x 1.5-2.5um given on this page at Mycobank.
The first photo and the sample were taken in the Wilderness, Whiteknights Park, Reading, UK, on 2013-01-11