Add 2 cups of yogurt and 1 1/2 cup of water to a blender and liquefy for about 2 minutes and keep aside. If you don't have a blender use a whisk to smooth the yogurt. You can adjust the water to the consistency that you prefer, in restaurents they often use 1:1 ratio of yogurt to water.
Add 2 tbs of oil to a non-stick pan and turn the stove to medium high heat
when the oil is hot reduce the heat medium, add the mustard seed and wait until most of the seeds popped about 1 minute. Add 1/2 tsp fenugreek.
Once the fenugreek is light brown, add red chilies. Stir for 15 sec. Add ginger, garlic, green chilies. Stir for 30 sec. Then add shallots and curry leaves. Make sure the stove is on medium heat and stir continuously until the onion is golden brown.
Once the onion starts to get golden brown, reduce heat to medium-low and add 1/2 tsp Turmeric Powder, 1/2 tsp chili powder, 1/2 tsp crushed cumin powder (optional). Stir for another 30 sec.
Caution(Once add the yogurt you should try the best not to stop stirring else the yogurt will form into curd and lumpy, consistency will be different)
Add Yogurt and STIR CONTINUOUSLY for 3-4 minutes under medium low heat, never boil(Check the spoon for signs of steam coming off the spoon). Immediately remove from the stove and continue to stir for another 2-3 minutes. Add salt to taste about 1 tsp
Store in a glass container and keep it in the Fridge. It should stay fresh for about a week. Enjoy with Rice.