Which of the following is served with fries?

Moules frites is the correct choice because it is a traditional dish that specifically consists of mussels (moules) served alongside fries (frites). This combination is commonly found in Belgian cuisine and is known for the textural contrast between the soft, flavorful mussels and the crispy fries. The fries serve as a perfect complement to the dish, as they are often used to soak up the broth from the mussels, enhancing the overall flavor experience.

The other options do not typically come with fries. Frisée salad is a type of salad made with frisée lettuce and is generally served as a starter or side dish, not with fries. Maison salad usually refers to a house salad that can feature a variety of greens and ingredients, also not typically accompanied by fries. An omelette Gruyère is a cheese omelette and is served on its own or with other sides but is not commonly paired with fries.