In a large bowl – ideally one with a pour spout, if you have it – whisk the eggs and milk until well combined, about 20 seconds. Whisk the flour, oats, and salt in a separate bowl, and add to the egg mixture. Stir with a wooden spoon or spatula just until the flour is incorporated. The mixture will still be lumpy. Add the melted butter, and whisk until the batter is smooth, about 30 seconds. Set aside at room temperature for 30 minutes. (This gives the gluten time to relax and brings the chilled ingredients closer to room temperature, so that the batter isn’t quite so cold when it goes into the oven.)

Note: If you don’t have a popover pan, you can use a regular muffin tin. Don’t use all 12 cups, though; use only the 10 outer cups. You’ll need extra oil to grease them.

While the batter rests, put ½ teaspoon oil into each cup of a popover pan. Adjust the oven rack to the lowest position, place the popover pan in the oven, and preheat to 450° F. After the batter has rested, remove the hot pan from the oven and, working quickly, distribute the batter evenly among the 6 cups of the pan. (If your bowl doesn’t have a spout, you might want to transfer it to a vessel that does; it’ll allow you to work much more quickly.) Return the pan to the oven. Bake for 20 minutes – and DO NOT open the oven door. Lower the heat to 350° F, and bake until evenly golden brown, about 15 minutes more. Remove the popovers from the pan and cool for 2 to 3 minutes before eating.