Preheat the oven to 400°F (200°C). Melt 1 tablespoon of butter in a 10-inch ovenproof skillet over medium heat.
Add the apple slices and cinnamon, and cook until the apples are tender, about 5 minutes.
In a large bowl, whisk together the eggs, flour, milk, and sugar until smooth. Pour the batter over the apples.
Dot the remaining tablespoon of butter over the top. Transfer the skillet to the oven and bake for 18 to 20 minutes, until the pancake is puffed and golden.
Notes
For added flavor, sprinkle with powdered sugar before serving.