CHRISTO'S LENTIL-SPINACH SOUP

2 cup diced yellow onions
1/4 cup olive oil
6 cup chicken stock
1 lb (2 1/4 c.) green lentils
1 lb chopped frozen spinach
or 1 qt. fresh leaves, stemmed, washed, and loosely packed
2 tsp ground black pepper
1/4 cup fresh lemon juice
salt to taste
Makes 6 servings.
In a deep saucepan, saute onions in olive oil until transparent, but not brown.
Add chicken stock and bring to boil. Add lentils and return to moderate boil.
If using frozen spinach, add it at this point; if using fresh spinach, julienne the leaves and add when the lentils have been cooking 20 minutes.
The soup should cook a total of 30 to 40 minutes,
depending on the dryness of the lentils.
Finish the soup with black pepper, lemon juice, and salt.