Preheat the oven to 350 degrees F. Butter the bottom and sides of a medium, round casserole dish.
In a heavy saucepan, bring the milk and cream to a gentle boil over medium heat. Slowly stir in the cornmeal. Continue to whisk vigorously (to prevent the cornmeal from clumping) until the mixture has thickened, 2 to 4 minutes. Turn off the heat and stir in the butter, Parmesan and salt. (If the mixture is very hot, allow to cool off for a few minutes.) Whisk the beaten eggs and baking powder into the cornmeal mixture. Beat with an electric mixer on medium-high speed until completely blended and smooth, 2 to 3 minutes. Pour the batter into the prepared baking dish. Bake until puffed and golden, about 35 minutes. Serve with lots of butter. (The spoon bread will collapse quickly as with most souffles, but will still taste perfectly delicious.)
If you can't find finely-ground cornmeal, process regular cornmeal in a blender for a few minutes until desired texture is reached. The finer grain yields a smoother spoon bread.