One of the interesting things in this box is the cards.
Here’s the back of this one:
From a box sold in Warminster, Pennsylvania.
Popovers That Pop
1 cup flour
1/2 teaspoon salt
1 cup milk
1 Tablespoon melted butter
Break eggs in mixing bowl. Add milk; sift in flour and salt. Beat five minutes. Add butter just before you finish.
Pour into buttered custard cups till half full. Place on cookie sheet in center of a cold oven.
Turn heat to 450 deg. for 15 minutes, then lower heat to 350 deg. to finish baking for one to one and a quarter hours (1 to 1-1/4 hours).