Meanwhile, in large 3 gallon stock pot, heat a glug of olive oil until shimmering. Add celery, carrots, onion, garlic halves, a sprinkle of salt, and, if using, mushrooms. Cook and stir occasionally to brown and caramelize, about 5 minutes or so. Add the ham hock, if using, peppercorns, parsley and bay leaves. Cook a few more minutes. Add wine to pot, stir up any bits and cook until it has evaporated.