cmyr's recipe above is quite excellent, but a few
notes for the sake of
pedantry:
Lentil soup
is perhaps even more popular in
Turkey than in Greece. The Prophet
reportedly said that lentils increase humility,
which is why large banquets (and humble lunches)
nearly always start with a bowl of lentil soup,
known as mercimek çorbasi in Turkish.
The type of lentil used makes a big difference.
Turks like red lentils, which cook relatively
quickly and dissolve into a purée while
doing so. The end result is a pleasing (and tasty!)
bowl of thick, smooth yellow soup. As red lentils have
a rather mild taste, go easy on the vinegar -- believe
it or not, a single teaspoon is plenty for two
quarts of soup.
You can also use green
or brown lentils, but they will require a longer
cooking time (I simmered mine 5 hours the last time
around) and they will always retain some of their
texture. While the end result is also quite tasty,
it's definitely a vegetarian meal that is just brown
gack, and probably not the type of thing you'd want
to serve to guests.
You can also add various things to (brown) lentil soup
to bulk it up: chick peas, tomato paste and
bulgur are all popular. For spices, try basil,
cayenne, coriander or mint. Lemon juice is
often substituted for vinegar.
For any lentil soup, some fresh bread on the side
is a nearly obligatory accompaniment. If reheating
the soup, add some water to re-liquefy it.