Coat 8 cups of a popover or standard muffin pan with nonstick cooking spray. Fill empty cups with 1/2 inch of water (so as not to burn pan). Heat oven to 450 degrees F.
In bowl, whisk together flour and salt. In second bowl, whisk together eggs and milk. Add to flour mixture; stir just until blended. Fold in cheese and scallions.
Fill prepared cups about 3/4 full (about 1/3 cup batter in each). Bake at 450 degrees F. for 15 minutes. Reduce oven temperature to 350 degrees F. and bake for 10 to 15 minutes, until browned and puffed. Keep oven closed until end of baking time or popovers will deflate.
Remove popovers from oven and immediately remove from pan. Pierce sides once with a knife to release steam. Serve warm. If needed, reheat at 350 degrees F. for 5 minutes to crisp outside edges. Makes 8 servings.