In the center of their courtyard stood a crooked, century-old mango tree. It produced the smallest, most stringy, unappealing mangoes in all of Delhi. But every June, Mr. Aiyar would make aam panna from those sour mangoes, adding roasted cumin, black salt, and mint from his garden. He'd distribute it to the entire lane—Hindu, Muslim, Sikh, Christian—in mismatched glasses.