1. Preheat oven to 400 degrees F. Place 10" cast iron skillet in the oven to heat with it.
2. Whisk together eggs, milk, flour, lemon zest, salt, and half of maple syrup.
3. Place butter in preheated skillet, swirling to coat the bottom and sides. Pour in batter. Bake until golden brown and puffed (20-25 minutes).
4. While the pancake is cooking, place apple slices, remaining maple syrup, cinnamon and nutmeg in a small pan. Cook over medium heat until apples are soft.
5. Serve cooked pancake hot and topped with apples.