To make these popovers, start with a cold oven. Butter a muffin tin and then spray it with baking spray (trust me, you need both).
Melt the butter. Whisk in the eggs, then the milk, flour and salt. Mix thoroughly.
Pour the batter into the buttered and sprayed muffin tins, filling them halfway.
Slide the pan into the cold oven. Turn the temperature to 450 and bake for 15 minutes (the oven will heat very gradually; that's exactly what you want).
After 15 minutes, turn the temperature of the oven to 350 and bake for another 15-20 minutes.
Remove from the oven and allow to cool, then remove from the pan/