Add lentils to the large stock pot. Add diced onions, butter, curry paste, curry powder, turmeric, garlic, ginger and cayenne. Stir until well combined.
Add tomato passata, water and stock cubes. Stir until lentils are fully covered.
Cover and cook on low simmering heat for 20minutes or until lentils are tender. Check periodically to make sure there is enough liquid for your lentils to soak up
Stir in coconut milk, salt and pepper.
Serve warm with some crusty bread.
Notes
The lentils break down quite nicely but if you'd like to puree with an immersion blender you can do so.