If you don’t have precooked potatoes, put the new potatoes in a pot of cold water. Add a bay leaf, then bring to a boil and simmer over low heat for 12-15 minutes until the potatoes are tender. Drain and let them cool slightly.
When the potatoes are cool, cut them into bite-sized pieces.
Heat the oil in a pan over medium heat, then add the garlic. Stir until light brown, then add the potatoes and the vinegar.
Let them sizzle and stir for a minute or so. Add the mustard and stir until the potatoes are well coated. Add about half a glass of water and the kale.
Cover and let it steam for about 5 minutes, or until the kale is tender.
Add the drained lentils and warm through for another 2–3 minutes.
Season with salt & pepper to taste.
Serve warm.