Slow Cooker Beef Bone Broth

vegetable or canola oil

Rumba Meats beef hind shank

Rumba Meats marrow bones ((about 4 2-inch pieces))

unpeeled carrots, (cut into 2-inch pieces)

unpeeled large onion, (quartered)

unpeeled garlic head, (halved)

green pepper, (cut into 2-inch pieces)

celery stalks, (cut into 2-inch pieces)

leek, (cut into 2-inch pieces)

beef bouillon ((optional))

bay leaves

whole peppercorns

kosher salt, (plus more after cooking to taste)

water