Double knitting is a cool knitting technique that allows you to produce a double layer of Stockinette Stitch fabric with mirror-image colorwork while knitting both layers at the same time.
It sounds complicated, and it certainly can be, but it's pretty easy to get started with double knitting once you understand how the fabric comes together, which is what this tutorial aims to do.
If you want to follow along, you'll need two different colored balls of yarn (one that you can get to both ends of) and knitting needles of a corresponding size. I used two medium-weight cotton yarns and a pair of size * US (5 mm) needles.
To begin, cast on the number of stitches you want to practice with. I used the two-color cast on, but for practice purposes you could just cast on with a single color, but remember that you need twice as many stitches as you intend to knit because you're working both sides of the fabric at the same time. So I have 12 stitches on each side or 24 loops total. Casting on with two colors actually makes it much easier to tell which "side" you're on, and it's not too difficult, so give it a try!
To start double knitting, you simply knit the first stitch in the color that it is (in this case yellow) with both yarns held to the back.