Place the ham hock and chicken stock in a pot large enough to accomodate both. Bring to a simmer and cook, partially covered for 1 1/2 hours. Remove the ham hock from the broth and allow both to cool slightly.

Bring a large pot of salted water to a boil. Cut the tough ribs and stems away from the collard greens and discard. Plunge the greens into the boiling water and cook for 10 minutes. Drain and cool slightly. Chop the greens coarsely and set aside.

Heat the oil in a soup pot over medium heat. Add the salt pork and cook until crisp, 3 to 5 minutes. Add the onion and celery and cook, stirring occasionally, until tender, about 5 minutes.

Add the flour and cook, stirring frequently, for 5 minutes. Gradually add the broth, whisking constantly to work out any lumps of flour and bring to a simmer. Add the collard greens, ham hock and sachet, simmer for 1 hour.

Remove the sachet. Remove the ham hock and cool slightly. Trim away the skin and fat, dice the lean meat and return it to the soup.

To serve, add the cream and season to taste with vinegar and Tabasco.