Combine the milk, Chicken Stock, salt, white pepper, and mace in a large pot over high heat. Bring to a boil, stirring occasionally. Whisk in the polenta. Once the mixture begins to thicken, reduce the heat to medium-low. Cook until the polenta is tender, stirring constantly with a wooden spoon and scraping down the sides of the pot, about 10 minutes. Add the Parmesan and stir to blend. Remove from the heat and stir to cool for 3 minutes.
Meanwhile, combine the eggs and egg yolks in a medium bowl and whisk until frothy.
Add 1/2 cup of the polenta to the eggs (to temper) and whisk to blend. Gradually add the egg mixture to the rest of the polenta (in about 3 additions), stirring constantly. Continue to stir vigorously for another 2 minutes. Reserve for the casserole.