A destination restaurant in West Philadelphia? It’s true — though you might miss it if your cabbie is driving too fast. Marigold Kitchen occupies the ground floor of a three-story Victorian that looks like every other house on the street (in fact, the place still boards lodgers). But the relative anonymity has helped turn Marigold into a cult favorite. Thirty-one-year-old Steven Cook specializes in creating high from low: Spanish mackerel transforms a piece of humble watermelon. A grilled Gruyere-and-caramelized-onion sandwich accompanied by a fried egg is elevated to extravagance by a bacony potato foam both savory and weightless. Cook’s pastry chef, Julia Kovacs, also knows how to surprise — a bittersweet-chocolate tart escorted by a dollop of sour-cream gelato hides a hint of smoked parika.