These flowers look like three petals over three sepals, maybe 2-3 cm in diameter, white with yellow centres, clustered along a stalk. Leaves look like Iris leaves. I think someone posted it with a name this spring, but I can't find that. These are a Parks Board planting, if I remember correctly.
Thank you both. Common names pale yellow-eyed-grass or satin flower. @Nik posted a different species last month, blue flowers: Virtual Garden Tour I certainly didn't remember the name from this posting by @Work in progress a year ago, and probably would not have figured it out from the bud photo with one open flower, but that completes the picture nicely: Plant identification