Bring half of the vegetable stock to the boil and add the lentils. Let simmer over a mild heat for 25-30 minutes.
Now peel and slice the potatoes, then cook like boiled potatoes.
Drain the lentil vegetables through a sieve.
Clean the spring onions and cut them diagonally into fine rings and sauté in the hot oil until translucent. Add the rest of the broth and bring to the boil, stir in the vinegar, bring to the boil and remove from the stove.
Add the potato slices and mix in the lentils. Let it steep for 30 minutes.
Cut the apple unpeeled into thin slices and mix immediately with the potatoes and lentils and season with salt and pepper.