Heat 30ml of the olive oil in a large saucepan over a moderate heat. Sweat the onion for 4-5 minutes, stirring occasionally, until softened. Add the garlic, cook for 1 minute, then add the cumin and garam masala. Stir well and cook for 1-2 minutes over a reduced heat, then stir in the passata, mixing well.
Add the lentils at this point, then cover with the stock. Increase the heat and bring to a vigorous boil. Boil for 5 minutes, then reduce to a simmer for 20-25 minutes. Remove from the heat and puree using a stick blender until smooth. Return to the heat, adjust the seasoning and stir in the cream, keeping the soup over a low heat.
Meanwhile heat the remaining olive oil in a frying pan over a moderate heat and toast the rye bread for 2-3 minutes, tossing occasionally until golden and crispy. Drain on kitchen paper. Ladle the soup into serving bowls and garnish with the croutons and a few split lentils if using.