On a medium-high heat, char the jalapeno directly on the flame. Once it’s blackened all over, remove from the flame and keep it aside to cool down.
Meanwhile, roast the garlic in a small frying pan on medium flame. Use a tong/spoon to press to brown and blacken in spots. Remove from the heat, roughly chop and keep it aside.
Once the jalapeno is cool to touch, scrape off the blackened skin using your hands (wear gloves if needed) or a knife .
Halve the jalapeno lengthwise, deseed & finely chop.
Next, in a mortar & pestle, make a paste of half the chopped jalapeno (since jalapenos can vary in hotness, start with half and more can be added later as per taste), half the onion, half the coriander/cilantro, garlic and half tsp of salt.