Wash a soak toor dal for 5-10 minutes. Cook Dal in pressure cooker or on stove-top, till soft and mushy.
Keep aside 1/2 apple, and puree the rest of apples with tomatoes, cumin seeds, peppercorns and green chilli.
In a pan, add ghee, when the ghee is hot add and saute apples, till soft. This will take around 5-6 minutes.
Once the apples are soft, add pureed tomatoes and apples.
Add asafoetida and turmeric. add salt as required. Cook it for another 5 minutes on low flame.
Meanwhile check Dal, mash the cooked dal with a ladle or masher.
Add Dal to the tomato-apple mixture.
Add 2-3 cups of water and let it boil for 2-3 minutes and turn off the flame.
Prepare the tempering.. In a pan heat ghee, add cumin seeds and mustard seeds.
Once the seeds crackle, add the tempering to rasam.
Serve hot garnished with chopped fresh cilantro. Squeeze in some lemon juice when serving it will enhance the flavour of rasam.