Melt the butter in a small pan and skim off the white foam to create clarified butter.

Pour the Calvados into a mussel pot and add the mussels as soon as the alcohol begins to steam.

Cook the mussels until all the shells have opened. Shake the pot occasionally to ensure the heat is evenly distributed.

Let the mussels cool slightly, then remove them from their shells.

In a large pan, sauté the apple and shallot in some butter until they become translucent, then add the mussels.

Lower the heat and stir everything together well, then gently fold in the parsley.

Divide the mussels between the jars and pour the clarified butter over them.

Let them cool down or place them in the refrigerator until the butter has reached room temperature.

The original recipe can be found in "My Little French Kitchen" by Rachel Khoo.