I develop recipes based on what I have on hand when I make them, so if you don't happen to have all the ingredients in my recipe, there's almost always some kind of reasonable and accessible substitute.

For instance - not everyone has fresh parsley on hand all the time (nor do I). A smaller quantity of dried parsley would work in lieu, of course, as would, say, 2 to 3 teaspoons of dried Italian herb mix in lieu of all the herbs I listed.

Some of the ingredient choices were quite deliberate - for instance, ketchup to bring that developed sweetness that's hard to achieve on a low slow cooker setting, fish sauce and Worcestershire to intensify the umami and give the sauce more depth of flavor, and stock to bring more richness, thickness and body than would water.

But if you don't have fish sauce, it's fine to just put a little more salt (like maybe 1/2 to 3/4 of a teaspoon). Even better to throw in a Tablespoon or two of a grated dry cheese like Parm, Romano, Asiago, or Manchego - here's a perfect use for the rinds! All the better to give the sauce the same kind of complexity and depth of flavor you would get from the funk of fermented fish sauce.

So many options I couldn't possibly go into all of them now, but you get the idea...