Heat oven to 425 degrees. In a medium bowl, whisk together eggs, flour, milk, salt, and nutmeg until well combined. Batter may still be slightly lumpy. (The batter may be made a day ahead and refrigerated overnight.)
Melt butter in a 12-inch cast-iron skillet over medium heat. Pour batter into pan, and transfer to oven. Bake until pancake is golden brown and puffy, 10 to 12 minutes. Transfer pancake to serving plate, and dust with confectioners' sugar. Serve immediately.