It’s amazing how you can take one ingredient, a chile, and extract so many levels of heat from it. Use it whole and unbroken: experience a wispy level of heat. Roast it to blacken the skin: watch its pungency creep up the heat scale. Coarsely chop it and then blacken it: break into a subtle sweat. The sweat-breaking version heats the curry here, but the starchy potatoes tone it down to make for a pleasant balance.