Preheat oven to 425 degrees F (220 degrees C). Place 9-inch cast-iron skillet in oven to warm it.
2
Mix milk and cornmeal together in small bowl and let soak for 10 minutes.
3
Sift flour, baking powder, and salt together in a mixing bowl. Beat cornmeal mixture, eggs, and butter into the flour mixture until you have a smooth batter, about 1 minute.
4
Remove skillet from oven. Swish vegetable oil in the skillet to coat; pour off excess.
5
Pour batter into the skillet.
6
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 18 to 23 minutes. Cut into wedges to serve.