Place the potatoes and onions in a large bowl. Drizzle them with 1 tablespoon of olive oil and season with the salt and pepper. Stir the mixture.
Place the potatoes and onions on a large sheet pan (at least 12 inches by 16 inches). Place in the oven and roast for 25 minutes, stirring occasionally.
After 25 minutes, add the sliced sausage to the pan. Return the pan to the oven, and roast for another 10 minutes, stirring occasionally.
Once the potatoes are tender and the sausage is cooked to an internal temperature of 160 degrees, drizzle the kale with the remaining tablespoon of oil, and then add the kale to the pan. Gently stir the mixture and cook for another 5 minutes, or until the kale is wilted.
Remove the pan from the oven and sprinkle with additional salt if desired. Serve warm.