I agree - low fat yogurt doesn't do the trick, always use whole milk. Still, I make my Mast a little differently. I dice (small) instead of shred, and I leave out the mint and onion, but the recipe's very similar. And I agree about the mint - if you're going to use it, use fresh mint! There's a world of difference!
This is good. I used vindalia onion, fresh mint from the garden, a four freshly ground pepper mix, sea salt, to taste, no other optionals. Made for Visiting Iran(Persia) in June 2012!