heat oil in a pan and crackle urad dal plit, chana dal, red chillies and peppercorns.
when the dal starts turning red, add onions and fry for half a minute
close and cook for a minute or two until it is transparent
add coriander leaves to this and fry until it shrinks
switch off and add tamarind and salt.
take it in a blender and grind to smooth paste
for tempering: heat oil, crackle mustard seeds, urad dal and curry leaves. let it turn crispy, add the tempering to chutney