Wash the potatoes and leeks. Peel the potatoes, cut in quarters lengthwise and slice into manageable pieces. Peel and chop the onions and leeks. Slice the bacon crosswise into small strips (lardons).
In a large soup pot, heat the olive oil over medium heat. Add the bacon, onions, and leeks. Cook, stirring for about 5/10 minutes until the vegetables and bacon are a little brown.
Add 1L of water, bring to a boil and add the potatoes, Provence herbs, French mustard, and cube bouillon chicken. Mix well, turn down the heat and let the soup simmer until the vegetables are tender for about half an hour.
Taste the soup before adding salt as the soup is already salty with the mustard and bacon. Season with pepper. Ladle the soup into shallow soup plates or bowls and top with grated cheese (Emmental/gruyère or comté). Accompany this soup with a piece of bread with French cheese.