Preheat oven to 425°.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and next 5 ingredients (flour through egg white); stir until moist.
Melt butter in a 10-inch cast-iron skillet over medium heat. Pour batter into pan; cook 1 minute (do not stir). Bake at 425° for 18 minutes or until golden. Sprinkle with powdered sugar, if desired. Cut into quarters; serve immediately.