Line a slow cooker with parchment paper and lightly grease with nonstick cooking spray. Turn the slow cooker to warm and set aside while you make the dough.
Add 3 cups of flour, sugar, yeast, milk, salt, and ¼ cup melted butter to the bowl of a stand mixer fitted with a dough hook. Mix together until the dough clings to the hook and is smooth and elastic. If the dough is too sticky, add more flour ¼ cup at a time until it is no longer sticky.
Divide the dough into 9 to 12 even pieces, depending on your desired roll size and the size of the slow cooker. Roll dough into round shapes with your hands. Add the rolls to the prepared slow cooker.
Cover the slow cooker with its lid and let it sit in the slow cooker on warm for 10 minutes. Then turn it to "high" and cook for 1½ to 2 hours, until the edges of the rolls are golden. (Note: If you would like the rolls to be more golden on top heat them under your broiler for 2 to 3 minutes).
In a small bowl mix together the remaining ¼ cup butter, garlic powder, parsley, and Parmesan. Brush the butter on top of the rolls. Break the rolls apart and serve warm.