This is an example of a few things. First, it is a yarn substitution tutorial. I took a simple double crochet in the round cowl I designed in Be So Fine (fingering weight yarn and D/3 hook) and converted the pattern for a much larger gauge with Be So Bold (worsted weight yarn and I/9 hook). Next, I decided to make the cowl a bit smaller as well. All of the math is spelled out in the video. And lastly, I also converted the pattern to be worked in a spiral instead of rounds, to avoid the joining and chaining where the rounds connect. This is a more seamless looking finished project and easy to do. This is also demonstrated in the video.
The patterns are similar, however the London Cowl features a 3-round crochet edging and the Simply Bold Cowl does not. If you wish to add the same edging to the Simply Bold cowl you will need to use a second skein of Be So Bold Yarn. All photos of this cowl are without the edging and it is a one skein project as shown.
Here is a video tutorial on crocheting the 3-round edging: