Wash potatoes thoroughly and cook in boiling water for about 20 minutes, drain, rinse and peel. In the meantime peel and finely dice the onions. For the vinaigrette, heat the oil in a pot and sauté the onions until translucent. Add bay leaf. Sprinkle with sugar. Deglaze with stock and vinegar, bring to the boil and simmer for about 10 minutes at low heat. Season strongly with salt and pepper. Remove from the heat.
Cut the potatoes into slices. Pour the vinaigrette evenly over the potatoes and let it stand for about 1 hour, mixing carefully several times. In the meantime, cook the eggs in boiling water for about 9 minutes, drain, rinse and rinse off the skin. Coarsely chop the eggs. Clean, wash and slice the radishes. Cut cheese into cubes. Wash and halve tomatoes. Clean, wash and finely chop lettuce. Cut cress from the bed.
Mix eggs, cheese, radishes, tomatoes and cress, except for something to garnish, with the potatoes. Season again with salt, pepper and sugar. On a plate sprinkle with remaining cress and arrange sprinkled pumpkin oil.