These have fabulous flavor, but I found the batter pretty dry and had to add more skim milk. (I did use fat free sour cream instead of the buttermilk though so that might have had something to do with it.) I filled my muffins almost to the top which was definitely not a good idea as they expanded A LOT. So fill half to 3/4 full only. Still, great flavor!
I substituted fat free sour cream for the buttermilk, and fat free cottage cheese for the ricotta. These muffins were very good and did not taste "low fat"!