• Whisk together the yogurt, besan, turmeric powder and red chilli powder to a smooth batter. 
• Heat the oil in a kadhai and add the asafetida to it. Over medium heat, pour in the yogurt batter and keep whisking. Whisking ensures that the sudden heat does not separate the yogurt.
• Keep cooking it on medium low heat and whisking every minute or so, till small bubbles start forming on top. 
• Add water to thin the curry out and keep cooking it, whisking every now and then, for about 30 mins.
• Now add the chopped spinach and salt, mix well and cook for 5 mins or so, till the spinach wilts.

For the tempered seasoning:

• In a smaller pan, heat the oil and add the cumin seeds to it. Once they sizzle. Add the garlic slices. Reduce heat to medium high. Once the garlic starts to crisp up, add the red chilli powder and pour this over the kadhi immediately. If you keep the red chilli powder in the hot oil for long time, it will burn.
• Serve hot with plain steamed rice.