Place a medium sized stock pot over medium heat and add corn oil, marrow bone and diced salt pork (or bacon). Cook til bacon is close to cooked through, about 5 minutes. For a vegetarian variation omit the bone and salt pork and use vegetable stock.
Add diced leaks, carrots and celery, bay leaf and garlic. Let it cook down for about 5 minutes. Strip the leaves off the fresh thyme by sliding the twig between pinched fingers, or just put the whole sprig into the pot, remembering to fish it out before serving. Let it cook another 5 minutes.
Add your stock. You can use any flavor of stock, picking the one you want based off the dish you're serving. If you're serving with mussels try a seafood or shrimp stock, and about a teaspoon of crushed red pepper. Add crushed tomatoes and let it simmer down and reduce for about 30 minutes.
Fish out the bay leaf and bone and any thyme twigs you left in.
