In a large bowl, combine the diced sweet potatoes and the blanched kale. In a large skillet, fry the bacon until it is brown and crisp. Drain out all but 1 tablespoon of the bacon grease. Fry the onion with the bacon until the onion is golden brown and tender, about 3-4 minutes. Pour this onto the potatoes and kale mixture. Fold in grapes. Deglaze the skillet with the vinegar, orange juice, oil, Tabasco, salt and pepper and bring to a boil. Pour the hot vinegar mixture over the potato salad and fold in, taking care not to mash the potatoes.

Serve warm.