For the collards: Add the stock, apple juice, onions, Cajun seasoning, bacon and collard greens in a large pot. Bring to a boil over high heat, then reduce the heat to medium and simmer for 1 hour. Then remove from the heat and drain the liquid from the pot, and allow the collards to cool.
For the potatoes: In a large pot bring 1 gallon of water to a boil, then add the potatoes and cook until softened, 15 to 18 minutes. Then drain. Press the potatoes, half of the flour and the butter through a food mill or ricer into a bowl. Next add the salt and white pepper, then blend with a whisk. Taste and add additional seasoning if needed.
To create the cakes, blend the potatoes with the collards in a bowl. Portion into 6-ounce cakes, about 4-inch rounds. To cook, heat a pan over medium-high heat, then add the oil. Dust the cakes with some of the remaining flour. Place the cakes in the pan and cook until browned, 3 minutes. Then flip and repeat process on second side, 2 to 3 minutes. Remove from the pan and serve.