This regional wintertime dish hails from Valle d'Aosta in the Italian Alps.
Adjust oven rack to middle position and heat oven to 250 degrees. Spread bread in even layer on rimmed baking sheet and bake, stirring occasionally, until dried and crisp throughout, about 45 minutes; let croutons cool completely.
Heat oil and butter in Dutch oven over medium-low heat until butter is melted. Add pancetta and cook until browned and fat is rendered, about 8 minutes. Stir in onion and salt and cook over medium heat until softened and lightly browned, 5 to 7 minutes. Stir in garlic and cook until fragrant, about 30 seconds.
Stir in cabbage, broth, and bay leaves and bring to boil. Reduce heat to low, cover, and simmer until cabbage is tender, about 45 minutes.
Adjust oven rack 6 inches from broiler element and heat broiler. Discard bay leaves. Spread half of cabbage mixture evenly in bottom of 13 by 9-inch broiler- safe baking dish, then top with half of croutons. Repeat with remaining cabbage mixture and croutons. Gently press down on croutons with rubber spatula until thoroughly saturated. Sprinkle fontina over top and broil until melted and spotty brown, about 4 minutes. Sprinkle with parsley and serve.