Heat the oil and butter
in a large
heavy-based saucepan until foaming. Add the onion and carrot and cook over a low
heat, stirring frequently,
for about
5 minutes until softened.
Add the lentils and garlic and stir well to mix,
then pour in the stock and bring to the boil.
Add the tomato puree, stir until
it is thoroughly
mixed into the liquid,
then add the marjoram and season with
salt and pepper to
taste. Half cover
and simmer gently for 30 minutes.
Pour half of the soup into a food processor or
blender and process until smooth, then return to
the pan of soup and stir to mix.
Add water to thin down
the consistency,
if
necessary,
then taste for seasoning. Serve hot, sprinkled with marjoram
leaves and grated Parmesan.