Preheat oven to 425. Beat the eggs at high speed with an electric mixer for 3 minutes, or until the mixture turns lemon yellow.
Slow the mixer to a crawl, and dribble in ½ cup of milk, taking about 20 seconds to pour it inches.
Into another bowl, sift the flour and measure 1 cup as exactly as you can, then add salt and baking soda and sift again. With the mixer still running on its slowest speed, add the dry ingredients to the eggs and milk.
Turn the mixer off and use a rubber spatula to make sure that all of the flour has blended in with the liquid.
Set the mixer to medium speed and dribble in the remaining milk. Blend for 1 minute.
Turn the mixer to its highest speed and beat for 10 minutes (or 5 minutes if you have a Kitchen-aid style mixer that uses a wire whip for beating). Extra beating won’t hurt.
Filter the batter through a fine-mesh screen strainer to remove any lumps, then pour into well-buttered popover cups or custard cups. (If you must use a muffin tin, fill only the corners.).
Bake at 425 degrees for 15 minutes. Without opening the oven, turn heat to 350 degrees and bake for 15 more minutes (20 minutes if your oven door has a window).