Heat the oven to 350°F and butter a 2-quart baking dish.
Bring the milk to a simmer, whisk in the cornmeal, and cook for 5 minutes until thick enough to leave trails.
Remove from the heat, stir in the butter and salt, and cool for 10 minutes before whisking in the egg yolks and baking powder.
Beat the egg whites to soft peaks and fold them into the cornmeal mixture in 3 additions.
Pour into the dish and bake for 35 to 40 minutes until puffed, golden and just set in the center.
Spoon into bowls within 10 minutes of leaving the oven.