These are wonderful. I need to make a comment about this recipe though. I use sourdough starter in my recipes and 'sour milk' does not make 'sourdough'. Soured milk is part of the leavening. You can use buttermilk or make your own sour milk by adding 1 T of lemon juice to a scant cup of milk.
The popovers came out perfect. I was skeptical because the batter seemed so thin, but they were beautiful and delicious. I did use fresh milk because I don't like sourdough though. Very tasty and pretty! Thanks for sharing!