Here it is:
30ml each oil and butter
2medium onions, chopped
3cloves garlic, crushed
2 sticks cinnamon
5ml ground cumin
10ml each ground coriander and turmeric
500ml red lentils, rinsed and drained
2 litres chicken stock
A little sea salt and sugar
30ml tomato paste
1 medium potato, pealed and coarsely grated
Thick plain yoghurt, garam masala and fresh coriander leaves to garnish
Heat the oil and butter in a large saucepan. Add the onions and garlic and when softening, add the spices. Allow them to sizzle for a minute or two, adding a dash of water if necessary to prevent scorching.
Add the remaining ingredients, except the garnish, bring to the boil, then cover and simmer gently, stirring occasionally, for about 25 minutes or until lentils and potato are soft and the. Gradients have cooked almost to a purée.
Stir vigorously to combine, and if too thick, add a little stock. Check seasoning, remove and discard the cinnamon and spoon the soup into warm bowls. Top each serving with a dollop of yoghurt, sprinkle with garam masala, and surround with a few coriander leaves.
The recipe also suggests serving in white bowls for prettiness factor! 
I usually skip the garam masala and coriander at end but the yoghurt is essential.