Put muffin tin in oven and preheat to 350 degrees F.
Bring eggs and milk to a warm room temp by putting eggs in very warm (tap) water for about 10 minutes and warming milk in microwave (only takes about 15 seconds).
In a blender cup (or blender if doing a large batch), blend eggs and milk. Add flour and salt. Blend again.*
When the oven has come to temp, carefully remove the muffin tin and add about 3/4 teaspoon butter in each muffin cup, making sure the sides are well buttered (a pastry brush works well). Quickly fill the cups half-full, then try to divide the rest of the batter equally.
Bake popovers until they are beautifully risen and browned, about 30-35 minutes.
DO NOT OPEN THE OVEN DURING BAKING TIME.
*If you don't have a blender cup, you can use an electric mixer, or even whisk by hand. But you want it really frothy.
