Preheat oven to 425°F. Place a 12-inch cast iron skillet inside to heat for at least 10 minutes.
In a blender or mixing bowl, whisk together eggs, milk, flour, maple syrup, vanilla, salt, and cinnamon until smooth. Let it rest while the skillet heats.
Carefully remove the hot skillet from the oven, add the butter, and swirl to coat the bottom and sides.
Pour the batter into the hot skillet and return it to the oven. Bake for 18–22 minutes, until puffed and golden brown.
Dust with powdered sugar, drizzle with maple syrup, or top with fresh fruit and Greek yogurt.