Schwabischer Kartoffelsalat (German Potato Salad - Schwabisch Style)

Place potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain; allow potatoes to cool slightly. Peel and slice potatoes. Mix potatoes and onions in a bowl; stir in mustard, salt, and black pepper.

Bring vegetable stock to a boil in a small saucepan, pour over potato mixture and stir to combine. Stir in vinegar and let rest for 10 minutes. Stir in vegetable oil and season with salt and black pepper if desired.