Soak tamarind in hot water for 15-20 minutes. Extract its juice and discard the pulp. We need 2 cups of tamarind extract. Wash, peel the skin and cut carrot into roundels. Soak tur dal in hot water for 20 minutes.(Though soaking is not necessary, I soak it always, as now a days, some dal varieties does not get cooked properly and also it saves a lot of time and fuel). Pressure cook dal and carrot for 3 whistles, adding turmeric powder. You can keep the carrot in a small vessel along with the dal. Alternatively, you can also cook carrots separately. Mash dal well with a masher. Heat oil in a pan, add mustard seeds, when it splutters, add fenugreek seeds, hing and curry leaves. Then add tamarind water, salt needed and sambar powder. Boil on medium heat until the tamarind water reduces and the raw smell of the tamarind goes. Add the mashed dal, carrot and 1/2-3/4 cup of water. Cook on medium heat until the sambar reaches a saucy consistency. You can adjust the consistency of sambar according to your personal preferences. Garnish with coriander leaves and serve hot with rice or even with idli and dosa.