Mini Cheese Popovers

Heat oven to 350 degrees F. In a medium bowl, sift together the flour and salt. In a microwave-safe measuring cup, heat the milk until warm but not hot, about 30 seconds. In the bowl of an electric mixer, whisk the egg on low until frothy. Increase the speed to medium and add the warmed milk. Gradually add the flour mixture, then stir in the chives. Place two 12-hole nonstick mini muffin pans on a large rimmed baking sheet and heat in the oven for 10 minutes. Remove from the oven and spray with nonstick cooking spray. Fill every other hole with batter (there should be 12 popovers total; the extra space is so the popovers have room to spread). Sprinkle the tops with the cheese and bake, rotating the sheet halfway, until puffed and golden brown, 45 to 50 minutes.