Casting off is over-rated - just graft together live squares to make a blanket. I suppose you need to like grafting though…

This is a good recipe for getting rid of a load of odds and ends. The edging is crocheted simply because to have a full size blanket on a circular needle would need something stronger than exists in this reality. If you live in an alternate dimension (or are making this in a baby size) a garter stitch edging would work equally well.