here is a link to a page also approaching modes starting with the major scale on the same root.

Not sure why Brian found this a gem. It is an approach that is used, though maybe I could have described it a little less clumsily. It starts with the major scale and describes the modes in terms of how they vary from it. It starts with Lydian, approached as major scale with a sharp 4th.

I did indeed learn it on a jazz course, but it is found in other contexts. For me it makes more sense than starting with C and going up through the notes C Ionian, D Dorian etc. I think it's a much better way of thinking about them if you set out to be able to hear the different modes in your head, but that may just be a personal thing.

Happy to hear more about why this was selected as a 'gem' though, if politely phrased.