Place the butter in your dutch baby pan (or whatever it is you have).
Make sure your oven rack is in the center, not anywhere else. Then preheat your oven to 400°F. Take your dutch baby/skillet/baking dish with the butter and put it into the oven. Keep an eye on it, because when it reaches about 250°F, the butter should be melted and you need to remove it from the oven.
You can do this while the butter is melting or afterwards, its up to you. But whisk the eggs and salt in a medium bowl, then add the milk. After that's mixed, whisk in the flour until its nearly smooth.
Take your now finished batter and pour your soon-to-be pannekoeken into your dutch baby/skillet/baking dish. Now put it back in the oven.
Bake for about 20 - 25 minutes (maybe longer if you used the baking dish or skillet). When the top starts to turn golden brown, it should be done. Its just me, but I do the fork test to make sure for thicker pannekoekens.
Serve hot with your favorite syrup, fruit, or other pancake topping. Pannekoeken are traditionally sprinkled with a little powdered sugar on top, but that's up to you if you want it.