Preheat the oven to 450°F (230°C), including the cast- iron skillet, placed on the middle rack.
In a blender, combine the milk, flour, sugar, salt, nutmeg, cinnamon, and eggs, and blend until uniform, about 30 seconds.
When the oven reaches temperature, carefully remove the hot pan from the oven and coat it with 1 tablespoon of the butter, working promptly to avoid burning the butter and cooling the oven. Pour in the batter and return the pan immediately to the oven.
Bake undisturbed for 15 minutes, resisting the urge to poke, stroke, or inspect.
Remove from the oven, place on a trivet, and put the remaining 2 tablespoons butter to melt on top.
Notes
Note An 8- inch or 10- inch (20- cm or 25- cm) cast- iron pan is crucial to your success here: the heat it retains, its nonstick attributes, and the straight and tall walls. Don’t attempt to make babies with anything less.