Heat the mustard oil in a medium pan or skillet over medium heat.
Once the oil is hot and shimmering, add the nigella seeds.
Let them sizzle for about 10-15 seconds until fragrant.
Add the green chili rounds and stir once, then immediately add the chopped kale, salt, and sugar to the pan.
Stir everything together to coat the kale, then pour in 120 ml (4.1 fl oz) / ½ cup of water.
Bring the mixture to a boil, then reduce the heat to low, cover the pan, and let it simmer for 5-10 minutes, or until the kale is perfectly tender.
Serve warm with rice, a dal or bean dish, and a side of yogurt relish.
Don't waste your stems! Finely chop the tender parts of the kale stems and add them to the pan a minute before the leaves for extra texture.
Adjust the spice level by slitting the chilies lengthwise for less heat, or removing the seeds entirely for a milder flavor.
