Place butter into a 12-inch cast-iron skillet. Put the skillet in your oven while it's preheating. The butter will melt and the skillet will get hot.
In a medium mixing bowl, whisk together the eggs, milk, flour, sugar, vanilla, and salt until smooth. The batter will be very thin and runny.
Once the oven is preheated, carefully pull out the oven rack your skillet is on. Pour the batter into the hot skillet.
Push the rack back in, close the oven, and bake for 20 to 25 minutes. The edges will puff up above the skillet and the center will be puffed and golden.
Remove from the oven and let your pancake sit for 2-3 minutes so the pancake can settle.
Cut the pancake into slices. Sprinkle generously with powdered sugar and serve with lemon wedges for squeezing, or top with butter and syrup. Cut the pancake into quarters or hoard the whole thing for yourself.
Notes
This recipe makes 1 pancake that serves 4 people with other breakfast items like eggs and bacon alongside. That being said, I can put a whole one of these down myself. So cook accordingly.