Turn oven to 425°F and place pan(s) in to preheat.
In a large measuring cup with a spout, combine eggs and milk, whisking until frothy. Add in melted butter and whisk until incorporated. If you like, you can use an immersion blender, blender, or hand mixer.
Add in flour, sugar (if using), and salt, whisking until smooth. if using a mixer or blender, just do it until smooth at this point. Let batter rest for at least 30 minutes, up to overnight.
If refrigerated, let the batter come to room temperature for at least 30 minutes before baking.
Remove pans from oven and add 1 tablespoon of oil to a large pan, or 1 teaspoon of oil to each individual pan, place back into oven for 5 minutes to preheat.
Individual Dutch Babies: Give the batter a quick whisk, then pour about ½ cup of batter in each pan. Bake about 15 to 20 minutes, or until deeply golden brown and well risen.
I like to dust the top of my Dutch baby pancakes with powdered sugar, adding a scoop of Greek yogurt that has been sweetened with a little bit of honey, and add some fresh berries.
Large Dutch Baby: Give the batter a quick whisk, then pour into your very hot 10 inch cast iron skillet. Bake for 20 to 25 minutes, or until deeply golden brown and well risen.
Slice and then garnish, or garnish the entire thing for a beautiful presentation and then slice and serve, adding more garnish to individual servings.