Soak cumin seeds and tuvar dal in 1/4 cup of water for 20 minutes. While the dal is soaking , let us prep the beets.
Wash, peel and cube the beets. Take it in a microwave safe bowl, add water to immerse the beets well. Microwave it for 10-12 minutes @ high for it cook. The beets must be fork tender. This can be done on stove-top also. Do not discard the beets water.
Let the cooked beets cool completely. Now take the cooked beets with the water, along with the soaked cumin and tuvar dal with the water, add chopped tomatoes, garlic, ginger, green chili, curry leaves and 1/2 cup of water. Blend them well with a stick blender or using a mixer jar. The liquid should be quite smooth.
Now take this blended liquid in a sauce pan, keep it in on the stove. Add rasam powder, turmeric powder and salt to this and mix well.
Let this cook in a medium flame, once it starts to boil, let it be on the stove for 10-12 minutes for the raw smell of the rasam powder to evaporate.
Once the rawness escapes, add 1.5 cups of water to this. If you feel the rasam is too thick, add another 1/4 cup to 1/2 cup of water to it.
Let this simmer in a slow flame for the rasam to froth well on top. Garnsih it with fresh coriander leaves and remove it from the flame.
Heat a small tadka pan with ghee, once it is hot, splutter mustard seeds, add cumin, hing and curshed peppercorns, crushed red chili, pour this sizzling tadka over the rasam.
Serve rasam hot/warm with rice , vegetable curry/appalam