I've looked at knot literature but haven't found a name for this, so I named it. The basic knot is well known; it's called a "lark's head". Since all I've done is to slip the two ends through the lark's head to make a noose, I call it that.
WARNING: Don't use this knot when human safety would depend on it. Climbers and mountaineers have well-tested, reliable knots for such situations.