Place a 10-inch cast-iron skillet on a rack in the middle of the oven and preheat to 425ºF. When hot add butter; meanwhile, place eggs, milk, flour, vanilla, salt, and nutmeg and cinnamon, if using, into blender and blend on high until well mixed. Pour into skillet over melted butter and bake for 18 to 20 minutes. Sift powdered sugar over Dutch Baby as desired, cut into wedges, and serve immediately.