Identify the Mushroom

Field note

Growing in a loose cluster from dark, well-composted soil at the edge of a vegetable garden bed, in full sun with no woody debris nearby. The caps are smooth, dry and pale ivory-white, rounded and firm when young; the gills beneath are tightly packed, pink in the youngest cap and shading to a deep chocolate-brown in the oldest. A thin, membranous ring encircles the short white stem, and the cut flesh blushes faintly pink where bruised. The smell is mild and faintly earthy, without any sharp or unpleasant note.