Place 12-inch cast-iron skillet in cold oven. Preheat oven to 450 degrees.
Crack eggs into a medium bowl. Add milk, flour, salt, and vanilla. Whisk everything together, but don’t over beat. Batter will be slightly lumpy.
When oven is preheated, place butter in skillet. Close the oven and wait for the butter to melt (it is okay if it doesn’t totally melt before adding the rest).
Open oven and sprinkle cinnamon on melted butter.
Pour batter in skillet and close oven.
Bake 20-25 minutes, or until puffy and golden brown.
Remove skillet from oven and transfer to serving plate. Sprinkle in lemon juice and powdered sugar.