Popevers finally popped

Half a dozen batches of popovers made in the last few months have failed to pop. They would come out edible enough, but without the high rise crustiness that makes a popover a popover.
Today it all came together and the popovers rose, got crusty, and were delicious.
The recipe is simple, cup of milk, cup of flour, two eggs, pinch of salt (1/4 tsp actually) and a tablespoon of melted butter. NO BAKING POWDER! Preheat oven to 400F. Add the milk, eggs and salt into a mixing bowl. Beat with an egg beater til smooth and fluffy. Melt the butter (I cheat and use margarine) in a big spoon on the stove. Beat the melted butter into the eggs & milk. Sift in a cup of flour. Only this time I used bread making flour instead of all purpose flour. It has more stickiness than the all purpose flour. Grease a muffin tin liberally, the popovers can stick and their hollow nature doesn't support prying out of the muffin tin. Bake 25 minutes at 400F, back off to 350F and give 'em another 15 minutes.
Yummy.