Heat a pan on medium heat, add poppy seeds and reduce heat to medium-low.
Carefully roast them until they are just a shade darker.
Remove from pan and cool.
In same pan, heat oil and add the mustard, fennel, cumin and onion seeds.
When they turn color, add the chillies and allow them to just blacken (but not burn, as that would impart a bitter taste).
Stir in the turmeric powder and immediately potatoes and salt.
Stir thoroughly and add the warm water (you may need to add more, but start with small quantities and add as you go along).
Cover and reduce to low heat.
Cook for a further 15 minutes until potatoes are tender.
Grind the cooled poppy seeds using a coffee grinder or mortar and pestle.
Stir the ground seeds into the potatoes – it will form a thickish paste which will adhere to the potatoes.
Continue to stir under medium heat if there is too much water, until you reach the desired dry-ish consistency.
Goes well with pooris or chapatis.