Crush them coarsely with a pestle. You can use grinder too for this purpose.
Transfer coarsely grinded mustard powder in curd.
Whisk the curd well.
Keep the bowl of curd under the sun for about 6 to 7 hours for fermentation.
Take a pan and add oil in it.
Let oil smoke first. Then off the heat and let the temperature of oil come down a bit.
Add red chilli powder, turmeric and salt. Mix well.
Add potatoes (boiled, peeled & cut into pieces) and mix them so that the spices coat them finely.
Remove the pan from heat & let potatoes cool completely.
Transfer these spiced potatoes into the bowl of curd.
Mix them well. Your auria is ready.
STORAGE
Keep it in refrigerator when not in use. It is served only cold.
Notes
1. In case mustard seeds are not available, use mustard paste or mustard powder instead.2. To get the best flavours, prefer to ferment the curd under the sun light only. But for any reason you can't do it, then leave the curd overnight for fermentation at some warm place in your kitchen.