You need to use plain Greek yogurt, not regular yogurt which is too thin and won't give you the correct results. I use a 6 ounce container of 0% fat Fage brand Greek yogurt that I pick up at Trader Joe's because for this recipe, I really cannot tell the difference between the 0% vs. full fat Fage Greek yogurt. Bottom line, just make sure it's a thick Greek yogurt and you'll be fine.