As cozy as a welcome hug, mac ‘n cheese defines comfort food. This creamy version brings comfort to both the eaters and the cooks. And you can make it in a snap with just a couple of ingredients. Forget measuring spoons or cups—the only unit is the “dollop.” And get this: you tell doneness not by time, color or temperature, but by the way it sounds. This recipephany comes courtesy of our sister-in-law Sheila, whose mother Ruth knew how to please her grandkids. Sheila’s children, Ariel and Eli (now with kids of their own), named it Grandma Mac to distinguish a unique dish that, as Eli puts it, offers “zero challenge to the palate…