Cook the grits following the package directions, using chicken stock or water, along with the salt, pepper, and garlic powder. Quick grits cook in about 5 minutes. If using stone ground grits, plan on extra cooking time.
Meanwhile, in a small bowl, whisk together the eggs and milk or half-and-half.
Heat oven to 350 F. Butter a 2 1/2-quart baking dish.
When the grits are thick, remove them from the heat and add the cheddar cheese, butter, and the egg mixture; stir until well blended.
Pour the grits mixture into the prepared baking dish and top with the Parmesan cheese, if using.
Bake the casserole for about 40 minutes, or until set.