In a large, deep skillet or pot, heat the olive oil with the butter over medium heat. Add in the onions and cook for 5 minutes, or until tender.
Add the collard greens to the skillet, and when the greens begin to wilt down, add the red pepper flakes and vegetable stock. Cover with a lid and cook for about 45 minutes, or until your desired texture is reached,* stirring occasionally.
At this point, add the garlic, and season with salt and pepper to taste. Cook for about 1 minute.
Add the heavy cream, Parmesan, and parsley. Stir everything well and cook for 1-2 minutes.