Sauté the Aromatics – Heat olive oil and butter in a large pot over medium heat. Add the chopped onion, leek, and carrot. Sauté for 3–4 minutes until softened.
Add the Potato and Lentils – Stir in the chopped potato and rinsed red lentils. Season with salt, black pepper, and cumin. Mix well.
Incorporate Tomato Paste & Liquids – Stir in the tomato paste, then pour in the boiling water or broth. Stir to combine.
Simmer Until Soft – Bring to a boil, then reduce heat and let it simmer for about 20 minutes, stirring occasionally, until the lentils and vegetables are tender.
Blend for Creaminess (Optional) – For a smooth texture, use an immersion blender to puree the soup. If you prefer a chunkier consistency, leave it as is.
Taste & Serve – Adjust seasoning if needed. Garnish with freshly chopped cilantro or parsley. Serve warm with a wedge of lemon and crusty bread.