Combine onion, celery salt and sugar in a large bowl. Add cabbage and combine well, massaging a little bit with your hands. Let sit 15 minutes. Drain off a little excess of the liquid in the bottom of the bowl if it looks like too much (like the cabbage is swimming in it).
Add vinegar and oil to cabbage and combine well. Season with pepper to taste and sprinkle almonds and blue cheese on top. Enjoy right away.
Note: The cabbage will shrink down in size as it wilts with the addition of the dressing.
Don't add vinegar, oil, almonds or blue cheese until you are just about ready to eat so that the cabbage with retain a bit of crunch, the almonds won't get soggy and the cheese won't dissolve into the dressing.