Place the potatoes in a stockpot and cover with cold water. Bring to a gentle simmer, add 1 teaspoon of sea salt, and cook until the potatoes are tender. Drain well.
While the potatoes cook, melt the butter in a saucepan over medium heat. Add the leeks and sauté until softened.
Add the cabbage and continue to sauté until tender, about 3-5 minutes. Stir in the kale, apple cider vinegar and sea salt, and cook for 2 minutes more. Remove from heat.
Add the cooked vegetables to the drained potatoes and mash. Fold in the heavy cream and black pepper until smooth and well combined.
