Mussels are a Belgian staple - cheap and abundant, they were originally considered a poor man's meal, and have been paired with fried potatoes for a long time at the country's famous friteries (fry shops). It is believed that the dish is originally from Belgium, because Belgians were the first to pair the mussels with fries, commonly eaten throughout the country in wintertime, when no fish was available.
Preparing moules-frites the Belgian way is very simple. Mussels should be sorted and cleaned before use, and broken ones should be discarded. Separately, prepare the sauce with butter and a mixture of finely chopped vegetables such as celery, leek, onion and shallots. The whole is flavored with thyme, bay leaf and black pepper.
Once the aromatic garnish is sweated, add the mussels and immediately cover the pot for steaming. By shaking the pot vigorously, the mussels are allowed to mix and open more easily. Finally, add the white wine and continue cooking for a few minutes. The mussels are ready as soon as they open. Those that do not open should not be consumed.
The proper preparation of the fries is essential. Choose a suitable variety of potatoes, otherwise they will disintegrate when cooked. Once washed, peeled and washed again, the potatoes should be thoroughly dried. They are then cut in sticks and then dried again.
The mussels are generally served in a pot and shared at the table. The fries are served separately to prevent them from getting soggy in the cooking juices from the mussels.
Moules-frites are usually eaten with beer or dry white wine.
According to 196flavors.com and en.wikipedia.org