This is a remake/rewrite of a vintage pattern called Square in the Form of a Cross published in 1899 in The Trove (Australia). The original was missing some instructional material and some whole rounds, and was very difficult to follow. The idea is not mine but I think you'll find my instructions much easier to work with.
I've taken the original, and changed the decreases to be more conventional (ssk in lieu of sl/k/psso) and lined things up more carefully.
There is also the suggestion and instructions for a crochet border; however, you could simply knit a few more rounds in reverse stockinette for size, incorporating judicious corner increases, if you wanted a completely knitted block.
Skills: working in round from outside in
working in round on dpn's or Magic Loop/2 circulars in small diameters
ssk, ssp (slip slip purl 2 tog), crochet bind off