Aloo Posto

A hot Kolkata afternoon and lunch is rice, dal and this. The potatoes have been fried gently until the edges go glassy, then the posto paste goes in and the flame drops right down. It stays pale, almost white. Two whole green chillies sit on the surface. At the end the pot is taken off the flame and one raw teaspoon of mustard oil is stirred through, and that smell going up is the whole reason people ask for aloo posto by name.

Wooden cold pressed black mustard oil carries this dish because there is nothing else in it to do the job. Pressed slowly in a wooden ghaani in small batches, it keeps the sharp, nutty pungency that heat destroys in a refined oil. You use it twice: hot at the start, taken to a light smoke and then brought down so the sting softens, and cold at the end, straight off the spoon, uncooked. That last teaspoon is not optional.

The one thing that decides this dish is the flame once the posto goes in. Keep it low and keep stirring. Poppy seed paste catches on a hot pan and browns in seconds, and aloo posto should stay pale and creamy. The moment it turns grey, the sweetness has gone and it tastes flat.

How to make it

1. Soak the poppy seeds in warm water for 2 hours, or in cold water overnight. Drain them in a fine strainer so no water is left behind. Wet seeds grind into a watery paste that will not cling to the potatoes.
2. Grind the drained posto with 2 green chillies and 4 to 5 tbsp water. Scrape the sides down and grind again. You want a thick paste that drops slowly off a spoon, a little grainy but not gritty.
3. Heat 3 tbsp mustard oil in a kadhai on medium-high until it turns thin and a light smoke rises. Lower the flame at once. If you are using onion, fry the slices for a minute until pale gold, lift them out and keep aside.
4. Add the dried red chillies and kalonji to the hot oil. Give them 10 seconds, until they crackle and smell toasty.
5. Add the potato cubes and salt. Fry on medium-low for 5 to 6 minutes, turning them now and then. The edges should go glassy and just start sticking to the pan. Do not let them brown.
6. Turn the flame to low. Add the posto paste, sugar and the turmeric if you are using it. Cook for 4 to 5 minutes, stirring almost all the time, until the raw smell goes and the paste clings to every cube.
7. Pour in 120 ml hot water and drop in the 2 whole green chillies. Cover and cook on low for 10 to 12 minutes, until a knife slides into a potato with no push. Add a splash of hot water if the pan looks dry.
8. Take the lid off and cook 2 minutes more until the gravy is thick and just coats the potatoes. Switch off the flame. Stir in the raw teaspoon of mustard oil and the fried onion. Cover and rest 5 minutes, then serve with hot rice.

Tips

• Buy posto fresh. We do not sell poppy seeds, so buy them from a shop that turns stock over quickly. Old posto tastes bitter and no amount of cooking will fix it. Smell a pinch before you buy.
• Grinding help: a small mixie jar works far better than a big one. If the blades will not catch, add 1 tsp raw rice or 4 soaked cashews. Both are old Bengali tricks and neither changes the taste.
• Make ahead: soak and grind the paste in the morning and keep it covered in the fridge. At night the dish takes twenty minutes.
• The mistake everyone makes: turning up the heat after the paste goes in, to hurry it along. Posto scorches in under a minute and turns grey and bitter. Low flame, keep stirring, and be patient.
• Storage: keeps 2 days in the fridge in a closed box. It tightens as it sits, so reheat with a splash of hot water.