In a saucepan, melt the butter and sauté the onion, sliced into julienne strips, until caramelized with a little salt.

Add the flour and mix well, then add the white wine.

When the alcohol smell is gone, add the broth and let it simmer for about 30 minutes.

Toast the bread with the cheese on top in the oven until melted, then place on top of the soup or melt the bread with the soup.