It's based on the traditional granny square stitch, but worked in stripes of red and blue.
You can see the detail here, that it's just three treble crochets into each gap then a chain stitch (and repeat, and repeat).
I did the stripes in countable rows, so that we go from 1 red row, up to 5 on the left.
To go along with the blanket, and to try my hand at a new skill (buttonholes) I also made these baby dungarees following a great tutorial at Me Sew Crazy:
I made a plainer version than the tutorial went for, omitting the front placket, but I was still pleased with the result. They're made of nice soft denim and lined with white cotton so that the legs can be turned up for baby if needs be.
The gifts went down well at the baby shower and will hopefully be useful and used!