Here's how to make the elusive bullion stitch!
First, with a hook appropriate to the yarn you're using, make a chain about as long as your bullion stitch will be tall (I did 5)
Then grab a smaller hook (I used a 3.25mm) and put it along side your working hook, butt-to-hook.
Make sure the smaller hook goes through the loop on your working hook - this will make a later step MUCH easier!
Yarn over a whole bunch of times (I did 10 yo)
Insert your working hook into whatever stitch you're working into (I inserted in the furthest ch from my hook). You may need to play with the yarn overs a bit to do this. Just be careful!
Pull through one loop
Pull through all loops on hook. I found it useful to very carefully pull through the first loop, then, making sure the smaller hook is butted right up against the tip of the working hook, hold onto the herd of yarn overs with your thumb and finger of your left hand, and pull the hooks through.
Take the smaller hook out
Yarn over (this will make a sort of vertical bar that ends up getting hidden behind the bullion stitch)
Pull through. Bullion stitch made!
Now do it again! And again! I did 7 more and then joined with a slip stitch to the top of the starting chain.
And here is the back; see the vertical bars?
Work around those vertical bars if you want to add more rounds that tuck behind the bullions, or work right into the tops of the bullion stitches.