The two most famous bartenders in the modern-day Blue Bar were Jimmy Fox, who worked days, and George Sroka, who had the night shift. Both of them had started there in 1946, before its renovation. When Fox retired in 1982, Sroka moved to days—and an ex-journalist from Brooklyn (by way of Los Angeles and Chicago) named David Grinstead took over in the evenings. Though Grinstead remained a writer at heart (he is the author of two novels, The Earth Movers and Promises of Freedom), he was also a first-class creator of cocktails, among them a stylish Sazerac, a textbook-perfect Sidecar, a dangerous but engaging “New York Margarita,” and, above all, what may well have been the world’s best Martini. This is his recipe.