The day before, cook 1000 g waxy potatoes until tender, about 20 min.
Briefly rinse with cold water and peel while still hot.
Let the potatoes cool and keep them loosely covered in the fridge until the next day.
The next day, cut or slice the potatoes into slices about 3 mm thick and place them in a large bowl.
In a nonstick pan, toast the 50 g pumpkin seeds over medium heat until the seeds start to pop.
Meanwhile, finely dice the 2 onions.
Set the pumpkin seeds aside, melt 1 tbsp butter in the pan and fry the 200 g diced bacon in it.
As soon as the bacon is lightly golden brown, add the prepared diced onions and sauté briefly.
Add 80 ml white balsamic vinegar or apple cider vinegar and 250 ml vegetable broth and bring briefly to a boil.
Add 2 tbsp medium-hot mustard as well as salt and pepper and simmer for 2 min.
Remove from the heat and stir in 2 tbsp vegetable oil.
Pour the still hot dressing over the potato slices and fold in gently.
Let the potato salad marinate for at least 1.5 hours (the longer the better), gently stirring every now and then.
Meanwhile, wash 100 g lamb's lettuce (mâche) and spin it dry.
To serve, mix the lamb's lettuce into the potatoes and season with salt and pepper. Divide among plates, drizzle each portion with about 1 tbsp pumpkin seed oil and sprinkle with the toasted pumpkin seeds.