Position a rack in the lower third of the oven and
In a large bowl, vigorously whisk the eggs and milk until frothy, about 1 minute. Add the flour and salt and stir just until incorporated (there will still be some small lumps in the batter, and that’s fine). Stir in the chives and cheese.
Remove the hot popover pan from the oven and spray it with nonstick spray.
Fill each popover cup two-thirds full with batter.
Popovers are best eaten while they are still warm, with a dab or two of butter.