Mix chopped onions, red chilli powder, sugar and salt. Grind them together to a coarse paste in a blender and keep it aside.
Heat oil in a pan over medium heat. Season with mustard and cumin seeds. Once they splutter, add black gram/urad dal and red chillies. Sauté till the black gram/urad dal turns golden brown, add a pinch of asafoetida and finally add curry leaves, stir for a minute and then add the ground onion mixture to it.
Stir occasionally till the oil leaves the side of the pan and raw smell goes away.
Turn off heat and allow it to cool and transfer to an airtight container.
You can refrigerate and use for about 3 to 4 weeks to serve with idli, dosa, pongal paniyaram, upma or combine with any meal..
Spice levels can be adjusted with chilli powder.
All the moisture in the chutney must be evaporated before turning off the heat.
Oil can be reduced if you are using up the chutney in 4 to 5 days.
You can increase quantities of the ingredients proportionally, prepare in large quantity to store in the refrigerator for about 3 to 4 weeks and serve with idli, dosa, pongal, paniyaram or combine with any meal.