Visiting a South Asian sweet shop during Diwali is a joyous and chaotic experience. Lines trail out the door. Employees furiously pack ornate boxes containing laddoos enriched with ghee, spongy rasgula and all manner of colorful sweets, often made with dairy, sugar and nuts and sometimes topped with a layer of edible silver foil. Friends and relatives meet around the display cases by happenstance, exchanging good wishes. Diwali, which will…