Finely chop the onion and garlic.
Peel and cut the potato into small pieces from about 1 cm on each side.
In a large saucepan, heat a generous drizzle of olive oil and sauté the onion for 6 minutes over low heat.
Add the garlic and sauté for another 2 minutes.
Add the tomato paste and the spices (turmeric, cumin, red pepper, cinnamon, salt and pepper), mix well and brown for 1 minute.
Add the lentils and diced potatoes to the pan. Cover with water up to 2 cm above your mixture.
Bring to the boil, then lower the heat and cover with a lid. Cook for 15 minutes, stirring occasionally, adding more water if necessary.
After 15 minutes, add the tamarind (or lemon) if you want to add a tangy touch to your dal, and cook for another 15 minutes over low heat, uncovered.
You can also add the tomato at this time if you put some.
Serve in soup plates, sprinkled with a few coriander leaves. Personally I always add a little sumac.
Accompany the dal with Iranian cooked basmati rice (see recipe on the blog) or naans or lavash type bread.