In a large bowl or measuring cup, whisk the eggs and milk until frothy, about 1 minute.
Add the flour and salt and whisk until completely smooth with no lumps. The batter should be about as thick as heavy cream.
Let the batter rest at room temperature for at least 30 minutes, or cover and refrigerate for up to 24 hours. Whisk again right before baking.
Heat the oven to 425°F with a rack in the center. Add about 1 teaspoon of beef drippings or oil to each cup of a 12-cup metal muffin tin, set the tin on a baking sheet, and heat it in the oven for 10 minutes, until the fat is very hot and shimmering.
Working quickly and carefully, pull the tin out and pour the batter into the cups, filling each about halfway. It should sizzle as it hits the fat.
Immediately return the tin to the oven and bake for 20 to 25 minutes, until the puddings are tall, puffed, and deep golden brown. Do not open the oven door for at least the first 20 minutes.
Serve right away with roast beef and plenty of gravy.
