Cook the whole mung beans
Make the buttermilk curry
Whisk the yogurt, gram flour, turmeric powder, optional asafetida, red chili powder, salt, and one cup of water in a mixing bowl until smooth with no lumps.
Heat oil in a saucepan on medium heat. Add the mustard seeds and cumin seeds and cook (watch carefully) until the mustard seeds start to pop. Add green chilis, ginger, and optional curry leaves, and cook for another minute.
Add the prepared yogurt mixture and the cooked mung beans, and stir well. Bring to a boil, and then turn the heat to low and simmer for 10 minutes, stirring regularly. Add more water if needed.
Turn off the heat and garnish with chopped cilantro. Another option is to stir the cilantro into the curry rather than using it as a garnish.