Pressure cook the soaked dal with turmeric powder for 4-5 whistles or 20 minutes
Meanwhile, extract the juice from the tamarind and discard the pulp
Add 3 more cups of water to it along with the shallots, radish, curry leaves, and sambar powder
Bring to boil and let it simmer until the radish pieces are tender, about 10-15 minutes
Add salt and cooked, mashed toor dal to this
Stir well to combine and heat until it just begins to boil
Heat oil in a small pan (or tadka pan), heat oil for tempering
When it starts smoking, add the mustard seeds
When they pop, add the shallots and hing
Fry until the shallots are golden brown
Dunk the entire tempering into the cooked sambar
Adjust salt as needed and garnish with chopped coriander leaves
I also add a pinch of sugar at the end, it enhances the taste quite a bit but mostly because my grand mom used to do that