Step 1

Place 3 large eggs and 1/2 cup whole or 2% milk in a medium bowl or blender and let come to room temperature, about 30 minutes.

Step 2

Arrange a rack in the middle of the oven and heat the oven to 425ºF.

Step 3

Peel 1 large Granny Smith, Honeycrisp, or Pink Lady apple. Halve and core the apple, then thinly slice.

Step 4

Melt 4 tablespoons unsalted butter in a 10-inch cast iron skillet over medium heat. Add the apple, sprinkle with 2 tablespoons of the granulated sugar, 1/2 teaspoon ground cinnamon, and 1/4 teaspoon ground or grated nutmeg. Cook, stirring occasionally, until the apples are soft and lightly caramelized around the edges, about 5 minutes. Meanwhile, prepare the batter.

Step 5

If mixing in the bowl, add the remaining 1 tablespoon granulated sugar, 1 teaspoon vanilla extract, and 1/4 teaspoon kosher salt to the bowl and whisk to combine, then whisk in 1/2 cup all-purpose flour until smooth. If using a blender, add all the ingredients to the blender and blend until smooth, about 10 seconds.

Step 6

Remove the skillet from the heat and spread the apples into a single layer. Pour the batter evenly over the apples.

Step 7

Transfer the skillet to the oven and bake until set in the center and puffed around the edges, 12 to 15 minutes. Serve dusted with powdered sugar or with maple syrup.