In a medium saucepan, bring the milk to a simmer. Gradually whisk in the cornmeal. Whisk over moderately low heat until thickened and bubbling, about 5 minutes. Scrape the mixture into a large bowl and let stand, stirring often, until warm. Whisk in the remaining 3 tablespoons of butter, the egg yolks and Parmesan, 1 1/2 teaspoons of salt and the baking powder.