Heat oven to 400° F. In a large bowl, whisk the eggs to combine. Add the flour and whisk until smooth. Add the milk, salt, and vanilla and mix until incorporated; set aside.
Add the butter to a large cast-iron skillet and transfer to oven until the butter melts. Remove from oven and quickly pour the batter into the hot skillet. Return to oven and bake until the pancake is puffed and golden, about 15 minutes.
Drizzle the lemon juice (if using) over the pancake. Spread the jam (if using) evenly over the top. Sprinkle with the confectioners' sugar.
