Casser la croûte means "to break crust" and these extra long crusty jambon-beurre sandwiches are ready to be shared.
La Grande Épicerie
Le Bon Marché Rive Gauche
Yesterday marked The Feast of Saint Aubin (Albinus d'Angers) who, along with Saint Honoré (Honoratus d'Amiens), is the go-to patron saint should you be a boulanger or pâtissier.