Lepista nuda

Common Name: Wood Blewit
Description: Cap 4-15 cm across, flattened-convex becoming depressed, wavy on the margin; bluish lilac then more brownish and drying paler; smooth, moist to dry. Stem 30-80 by 10-25 mm high and wide.
Habitat: scattered or in groups on compost or organic debris in open areas, gardens, under bushes, and along paths. Common and abundant. Found widely distributed in North America.
Edible: excellent.

Source: Mushrooms of North America by Roger Phillips.