Add rinsed millet and moong dal to the Instant Pot inner pot. Add 2 cups water, turmeric, and salt. Stir to combine.
Secure the lid and set the valve to Sealing. Cook on High Pressure for 8 minutes.
When the cook time ends, let pressure release naturally for 5 minutes, then switch the valve to Venting for a quick release.
Open the lid and stir well. The pongal should be soft, mushy, and creamy. If too thick, add 2-3 tbsp warm water and stir.
Set the Instant Pot to Sauté mode (or use a separate small pan). Add ghee and heat until shimmering.
Add mustard seeds and wait for them to pop, about 30 seconds.
Add cumin seeds, peppercorns, and hing. Stir for 15 seconds until fragrant.
Add ginger and green chilies. Sauté for 30 seconds until the ginger turns lightly golden.
Add cashews and fry, stirring, until golden, about 1 minute.
Add curry leaves and stand back; they will spit in the hot ghee. Let them crisp for 10 seconds.
Pour the tempering directly over the pongal and stir well. Taste and adjust salt.