- Preheat oven to 325F. Beat butter in a large mixing bowl with an electric mixer on medium to high speed for 30 seconds. Beat in powdered sugar and cocoa powder until combined, scraping side of bowl occasionally. Beat in coffee liqueur and vanilla. Beat in as much flour as you can with the mixer. Stir in any remaining flour, 1/2 cup of the round hazelnuts, and ground coffee beans with a wooden spoon.
- Shape dough into 1-inch balls. Roll dough balls in remaining ground hazelnuts. Place balls 2 inches apart on ungreased cookie sheets. Bake in preheated oven about 15 minutes or until bottoms are lightly brown. Lightly press a whole coffee bean onto the top of each cookie. Cool on cookie sheets on wire racks for 3 minutes. Transfer cookies to wire racks and cool completely. Makes 54 balls.
From the Test Kitchen
To toast hazelnuts, spread them in a single layer in a shallow baking pan. Bake in a preheated 325F oven for 15 to 20 minutes or until nuts are slightly golden brown, stirring once or twice; cool completely. Grind nuts and set aside.
Place cookies in layers separated by waxed paper in an airtight container; cover. Store at room temperature for up to 3 days or freeze for up to 3 months. Thaw cookies, if frozen, before serving.