Heat the butter until it bubbles over medium-low heat, then stir in the flour. Make a light brown roux, stirring constantly to avoid burning.
Add the ham, green onions, shallots, and garlic, and sauté until the vegetables are soft. Add the wine and bring to a boil, whisking to dissolve the roux into the wine. Reduce the wine by about half.
Add the beef stock, marrow, bay leaf, Worcestershire and thyme, and bring to a boil. Reduce to a simmer and cook, stirring now and then, for a half hour to 45 minutes, until a sauce consistency is achieved. Don't over-thicken.
Add salt and Tabasco to taste. Remove the bay leaf.
