Preheat oven to 350°. Cream butter and add the sugar. Mix in egg yolks, vanilla, and flour. Roll dough into logs. Use a fork to make indentations into the logs. Bake for about 11 min. When the cookies cool you can break the bigger logs into smaller (more bite-sized) pieces.
Frosting
Cream the butter. Mix in the powdered sugar, cocoa, coffee, and vanilla. Add a few drops of green food coloring into a bowl with a couple tablespoons of water. Add the walnuts to the food coloring mixture, then take the walnuts out and put then on a lined cookie sheet. Bake the walnuts for about 6 minutes to dry them out. Frost the cookies on both ends and dip the ends into the green walnuts
Recipe by Blissful Whisking at https://blissfulwhisking.com/chocolate-log-cookies/