This takes about an hour or so to make and then cool, so it’s the place to start. That’s good because you can prepare the eggs at the same time.
So, set a medium size saucepan onto a low heat and add the chopped mango, all its juice, and the salt. Stir, and let it cook low and slow until it just begins to barely bubble. Add the serranos, onion, garlic, sugar, mustard seeds, and apple cider vinegar. Take some care to stir it all occasionally on that low heat, so the onion melts down into the mango - about 5 minutes. Good.
Now stir in all the remaining spices - sumac, fenugreek, paprika, cumin, and turmeric. Let the pan just barely simmer for another 5 minutes. You’ll find the mango chunks starts to break down a little as you watchfully stir the pan, and that the whole mix will be pretty thick. I say watchfully because you want to keep the mixture gently stirred just enough to stop it sticking to the bottom. Also, you’re not looking for a puree here, but rather to keep some texture in your amba chutney.
Now stir in the water, and let the pan come up to a very slow simmer. As soon as that happens, cover the pan with a good-fitting lid and let it simmer away very gently – and I mean very gently - for 25 minutes. Give it a few slow stirs as its simmering to make sure it doesn’t catch on the bottom.
Remove from the heat, stir in the lemon juice and let it slowly cool right down. Once cooled, pour into a serving bowl. Done.