In a medium bowl, combine flour, almonds, hazelnuts, and cocoa powder; set aside. In a large bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add sugar and vanilla. Beat until combined, scraping bowl occasionally. Add the flour mixture, beating on low speed just until combined. Cover and chill for 2 hours or until dough is easy to handle.
Preheat oven to 350 degrees F. Shape dough into 1-inch balls. To shape crescents, roll each ball into a short log with tapered ends. Curve log slightly into a crescent shape and place crescents 1 inch apart on an ungreased cookie sheet. Bake in the preheated oven for 15 to 17 minutes or until edges are set. Transfer cookies to a wire rack; let cool.
Drizzle melted chocolate over cooled cookies. Let stand until chocolate sets. Makes about 48 cookies.