There are many classic cocktails that are variations of the Martini and Martinez, but few go beyond the addition of a liqueur or juice. When I came across the Biltmore recipe in Just Cocktails I knew there was something special to this drink.
Two factors make this drink extraordinary in comparison to many of its contemporaries: fresh pineapple and a hazelnut soaked in maraschino. Through some experimentation I have found that muddling the pineapple into small pieces and releasing the juice, then stirring it with the classic gin and vermouth (with maraschino) combination allows just enough fruit flavor to be released for a balanced drink. It's a refreshing touch that is a nice turn from a Dry Martini.
It took a bit of searching, but I was able to come up with a link between the name of the cocktail and the hazelnut garnish, which seems out of place but is actually a nice touch. The connection could start with The Biltmore Estate in Asheville, North Carolina and that area's native American hazelnuts, which are plentiful there. That is just one theory, and like many cocktails we may never know the true story behind the drink.