Grind walnuts in a food processor until almost powdery; set aside.

Grind chocolate in a food processor or blender until powdery; set aside.

Preheat oven to 275 degrees.

Combine butter and sugar in a mixer bowl and beat until fluffy and well-blended.

Add vanilla and chocolate, mix thoroughly.

Gradually fold in flour, then walnuts, until well-combined.

Drop cookies by heaping teaspoonfuls onto ungreased or parchment-lined baking sheets, placing them slightly apart.

Bake until cookies are hard and lightly browned (35 to 40 minutes).

Let cookies stand on baking sheets for about 5 minutes before removing them to wire racks to finish cooling.