Position an oven rack to the lowest level in the oven and preheat the oven to 450° F. (Make sure the other rack is removed or at the top of the oven, as the popovers will rise dramatically while baking.) Spray a 6-well popover pan with cooking spray.
In a blender; blend together the eggs, milk, and salt on medium-high speed until well combined, about 15 seconds. Add the flour. Blend on medium-high until smooth, about 15 seconds. Add melted butter, blend on medium-high until frothy, about 15 seconds.
Immediately pour the batter into the prepared pan, filling each well. Place on a rimmed baking sheet to catch any drips in the oven.
Bake on the lowest oven rack for 20 minutes. Without opening the oven, reduce the temperature to 350°F, and continue baking until deep golden brown, about 18 to 20 minutes more. Immediately after they come out of the oven, gently puncture each popover in the center with a pairing knife and remove from the pan. Serve warm.
Make sure to measure your flour correctly. I highly recommend always using a scale to measure. However, if you don’t have a scale, do not scoop the flour directly from the bag. Be sure to fluff your flour with a spoon and then spoon it into your cups before leveling it off with a knife. This method is the best way to measure flour without accidentally overpacking the measuring cup.
The eggs should be at room temperature to ensure they are evenly and quickly incorporated into your batter. This helps the batter from being overmixed. If you forgot to bring out your eggs, you could quickly bring them to room temperature by placing them in a large bowl and covering them with warm tap water for 5 minutes.
When spraying the popover pan, be sure to spray not just the wells but also the tops. As the batter will rise and overflow, you don’t want them to stick on the top of the pan.
While you might want to peek while these beauties bake, don’t! Opening the oven door might lead to the popovers deflating.
Don’t skip readjusting the racks in the oven. Other than the risk of the batter rising to the next rack, you don’t want the popovers burning if they get too close to the heat source.
You must gently puncture each popover in the center with a pairing knife to allow the steam inside of them to escape. If you do not cut into them, they lose their crispiness.