Pressure cook the lentils (dhal) till it is soft and mushy ( I keep it on for 2 whistles and then let the cooker sit for 10 minutes so the dhal continues to cook in the steam after the stove is turned off). The amaranthus leaves, cleaned as in step 2 below, could also be steamed when the dhal is cooking, though I prefer to cook them separately as they get overcooked in the pressure cooker.
Meanwhile pick the leaves off the stems of the amaranthus as well as any tender stems. If cooking with Tender amaranthus (Thandu keerai), most of the stem can be used. Wash them several times until all the grit and sand have been completely removed. Chop into small pieces.
Cook the chopped leaves and the chopped tomato in as little water as required to just cover them while cooking (about 7- 10 minutes on medium flame, but keeping looking out that the water doesn't dry out). Add salt to taste.
Grind the coconut paste with all the ingredients listed above, with as little water as required for a smooth paste.
Add the paste to the cooked dhal and whisk till smooth and the individual grains of dhal are not visible.
Add the dhal and coconut paste to the cooked dhal, stir well. If the kootu is very watery, boil till the excess water evaporates.I like the gravy a little fluid and not thick.
Take off from the stove, set aside and cover.
Heat oil in a small pan (kadai).
Burst the mustard seeds, add methi (fenugreek) seeds and let them burst (10 secs). Add jeera (cumin) seeds and sauté for 10 secs.
Add the dry red chilli, turn it around after 5 secs so that both sides fry in the hot oil.
Add curry leaves and turn off the stove.
Pour the tempered oil on the kootu.
Serve with rotis or with rice and rasam or with vathalkuzhambu or with rice and dhal.