Cream butter and sugar using an electric beater for about 1 minute or until smooth and creamy. Add yolk and vanilla, cream for another minute.
Add minced walnuts, flour and salt. Continue mixing until it forms a dough. Tip: To mince walnuts, add walnuts into a food processor and process until they are finely minced.
Shape dough into a flat disc and roll between two sheets of parchment paper, until slightly less than ¼ inch thick. Transfer dough, along with parchment papers, onto a baking sheet and place in the refrigerator for at least 4 hours (up to one day), until firm.
Shape cookie
Remove dough from refrigerator, cut circles using a 3-inch round cookie cutter.
Place one round one a work surface and using the same cookie cutter, cut the 2 opposite sides, to make tree trunk (refer photos and video). Place one cut end over one end of the tree trunk, pressing slightly to adhere.
Using a butter knife, cut about ¼-inch slits on the bottom of the tree top to create a fringe.
Repeat process to shape remaining cookies and place them in a parchment lined baking sheet. Place baking sheet back into the refrigerator and chill until firm, at least 2 hours.
Bake
Preheat oven 325°F.
Bake cookies for 20 to 25 minutes, or deep golden brown in color. Place baking sheet on a wire rack to cool completely.
Decorate
Melt chocolate chips in a microwave, until melted and smooth, about 30 to 60 seconds.
Using a small spoon, spread some melted chocolate on the tree tops.
Using a tooth pick make a fringe pattern on the base of the tree top (refer photos and video).
Press one candy eyeball on the chocolate. Let stand until the chocolate sets.
Video
Notes
Chop walnuts very fine - Ensure that no walnut pieces are larger than ¼-inch , avoiding coarse pieces and preventing making them into a fine powder.Chill dough – I recommend chilling both the rolled dough and shaped Halloween trees for several hours, which gives ample time for the dough to firm up before baking.