Few chefs think harder about what they cook than John Shields, who helms the kitchen of this sophisticated, tasting-menu-only spot. Shields is a kitchen wonk, prone to intellectualizing his cooking in a way that takes after his former boss, Grant Achatz. But Shields’s own particular wizardry is less about exploding expectations and more about coaxing purity of flavor from his ingredient of choice. Take, for instance, a dish referred to on a recent menu as Seawater: a clear, briny broth extracted from seaweed and mussels, the essence of the ocean itself. Karen Urie Shields, his wife, runs an equally focused pastry program. Its hallmark is a single golden egg yolk, cured in molasses and star anise, set atop a cloud of whipped frozen yogurt meringue that obscures a crunchy farro crumble underneath. Like much else at Smyth, the flavors may be down-to-earth, but the presentation is otherworldly.