Sauté half the onion in 3 tablespoons of oil in a large
saucepan over medium heat for 2-3 minutes, or until
softened.
Add the cumin, coriander, red pepper flakes, and garlic
and mix well. Cook for 2 minutes.
Add the lentils, carrot, and celery leaves, reserving a
few to garnish.
Pour in the stock and cook for
35-40
minutes, or until the lentils have broken down.
Add the lemon juice and season with salt and pepper. If
the soup becomes too thick, add a little water to thin
it.
Sauté the remaining onion in the remaining oil in a
small frying pan for 5-10
minutes, or until very tender and golden brown.
Ladle the soup into serving bowls and garnish with the
onions and reserved celery leaves.