Lightly coat a 6-quart slow cooker with nonstick spray. Add the polenta, broth, water, half-and-half, salt, and garlic powder, and stir to combine.

Set the slow cooker to low heat and cook for 4 hours, stirring occasionally if possible to prevent sticking.

When the polenta is soft and creamy, stir in the butter and Parmesan cheese. Cover and let sit for a few minutes until melted and combined.

Give the polenta one last stir, adjust seasoning if needed, and serve warm. Note: The polenta will continue to thicken as it sits. If it becomes too thick, whisk in a little more half-and-half or warm water until it reaches the desired consistency.