Start by seasoning the osso bucco shanks with salt and pepper. Heat cooking oil in a large pan over medium-high heat. Once the oil is hot, add the osso bucco shanks, searing both sides. Transfer the seared shanks to an instant pot.

In the same pan, melt the butter and sauté the onions until they soften. Add red wine to deglaze the pan, ensuring to scrape up any flavorful bits. Stir in dried parsley, thyme, oregano, and rosemary. Next, add the garlic cloves. Add the beef stock and bring the sauce to a boil then remove from the heat.

Transfer the onion and herb sauce to the instant pot with the osso bucco. Cook under high pressure for 55 minutes. Once done, allow a natural pressure release for 20 minutes.

Remove the osso bucco and garlic cloves using a strainer. Transfer the meat to one bowl and the garlic cloves to another. Debone the osso bucco and transfer the bone marrow to the bowl with garlic. Mash this mixture to form a paste, seasoning with sea salt. Mix in the mayo to get a creamy garlic-marrow mayo.

Skim any excess fat from the sauce then return it to the pan. Simmer until the sauce reduces by half. Add in the osso bucco meat and continue to simmer until you achieve a sticky glaze.

Drizzle ciabatta slices with olive oil and toast both sides in a pan. Once toasted, slather both sides with the garlic-marrow mayo. Pile on the glazed osso bucco meat on one slice, sprinkle cheese, and top with the other slice of bread. Slice the sandwich in half and serve immediately.