A very interesting topic! And to make things even more complicated, there are the diets espoused by people like Sally Fallon, who advocate lots of animal fats--lard, butter, organ meats, etc. I will say, though, sometimes science, especially nutrition science, seems almost like religion. It’s more about what you believe than what the “facts” are!

You can absolutely do without the buttermilk powder. I liked the extra tang it gave the dressing, and it also helped thicken it a bit. However, if you wanted to use buttermilk for part of the yogurt, you could do that. You could also substitute dry milk powder for the buttermilk powder (it wouldn’t alter the flavor--just the texture).
If you’re interested in finding buttermilk powder, Bob’s Red Mill sells it ( http://www.bobsredmill.com/sweet-cream-buttermilk.html ).

So glad you liked it, vintagejenta! I heartily agree. Just this afternoon, I cooked up a pot of white limas, and they have the most wonderful, slightly sweet flavor. We’re going to sauté them tonight with some fried sage, tomato, and pasta for a rudimentary pasta e fagioli.

Just before adding the okra to the oil. Sorry!