Sauté the garlic and onions in the butter in a large stockpot until the onions are translucent and just beginning to brown. Add the flour. Cook for 3 to 4 minutes over medium heat, stirring constantly. Add the oysters and water. Bring just to a simmer. Cook over low heat for 1 ½ to 2 ½ hours. Add the bay leaves, thyme, salt, pepper and Tabasco sauce. Cook for 30 minutes. Add the half-and-half. Cook until heated through. Do not boil. Discard the bay leaves. Serve immediately.