Pick lentils, wash in running water and soak for at least 30 mins.
Scrape, wash and chop ginger.
Peel and chop garlic.
Peel, wash and chop onions.
Remove stems, wash, slit, deseed and chop green chillies.
Wash and chop tomatoes. Clean and wash mint.
Put the drained lentils in a utensil, add salt and water (approx. 2 litres/8 1/3 cup), bring to a boil, reduce to low heat and remove the scum.
Add two-thirds each of ginger and garlic, cover and simmer until the dals are cooked and two-thirds of the liquid has evaporated.
Mash the lentils lightly against the sides with a wooden spoon. Adjust the seasoning.
Heat oil in a wok, add onions and saute over medium heat until light brown.
Add the remaining ginger and garlic and saute until onions are brown.
Then add green chillies, stir for a minute, add tomatoes and fry until tomatoes are mashed.
Transfer the lentils, stir for 2 mins, then cook until medium-thick consistency is reached. Remove to four individual bowls, garnish with mint, top with a knob of butter and serve as an accompaniment .