Maybe you know this as a Dutch Baby or a German Pancake or as Yorkshire pudding. In our house we call it Baked Pancake, and we make it all the time. The yummiest way to eat this is to sprinkle it with lemon juice and sieved powdered sugar, but we usually eat it in big hand-held wedges, utterly plain or spread with jam.
Heat the oven to 425ºF, then put the pan in to heat while you prepare the batter. A 10- or 12-inch oven-proof skillet is ideal, but you could use a comparably-sized baking dish (Pyrex, say).
Now use a whisk to beat the eggs in a medium-sized bowl, then beat in the milk, then the flour and salt. We tend to beat the mixture until it's just smooth.
Now pour the batter into the buttery pan and return it the oven. Set your timer for 15 minutes. We bake it for 20, but I think it's worth peeking at it at 15 because your oven might be different from ours: you want it to be puffed and golden and quite brown in places.
The only trick here is that the pan be very, very hot before you melt the butter and pour the batter in: that's what will make the pancake puff.