That’s macarons, not macaroons. And the “o” makes all the difference. Though technically the spellings are interchangeable, the recipes rarely are. The two-o is a familiar Philadelphia confection, a dense deli cookie packed with coconut and often dipped in chocolate. The single-o is a delicate Parisian favorite, two fragile almond-meringue rounds sandwiching a thin layer of bittersweet ganache or luscious jam. The current trend on the other side of the ocean is macarons in a rainbow of bold colors and flavors (Green tea? Licorice?), but at Stephen Starr’s new Rittenhouse brasserie Parc, pastry chef Frank Urso hews to such classic French flavors as chocolate, lemon, pistachio and raspberry.