French Onion Soup au Gratin with Gruyère

Preheat the oven to 190 °C.

Cut the baguette into slices about 6 mm thick, spread them on a baking sheet, and toast in the oven for 5–7 minutes until golden brown. Set aside.

Prepare a bouquet garni: Cut off about a 10 cm long green piece from the washed leek. Wrap the bay leaf, thyme, and parsley stems in it and tie tightly with kitchen twine.