In a medium bowl, combine the apple, blue cheese, celery, mayonnaise, and lemon juice. Stir gently to combine. Season to taste with salt.
To assemble, mound a small spoonful of the apple mixture onto the core end of each endive leaf. Sprinkle with the hazelnuts and serve.
Make Ahead Tips
To bring this hors d'oeuvre to a party, pack the apple mixture, the endive, and the hazelnuts separately and quickly assemble them once you arrive (don't make the apple mixture more than an hour ahead). Also, you can toast and chop the hazelnuts for up to one month in advance and freeze them in an airtight container.
nutrition information (per serving):
per piece, based on 40 pieces;
Photo: Scott Phillips