Preheat the oven to 450 degrees F.
Generously grease popover pans (6 cup) with softened butter.
Place the pans in the oven for exactly 2 minutes to preheat.
Meanwhile, whisk together the flour, salt, eggs, milk, and melted butter until smooth. The batter will be thin.
Fill the popover pans and bake for 20 minutes. Lower to 350 and bake for another 20 minutes. Do not peek.
Once removed, take out of pans and make a tiny slit with a paring knife on the sides to release steam.
Adapted from Ina Garten