Cream together the softened butter and granulated sugar in a mixing bowl until the mixture is light and fluffy, and smells subtly sweet, about 2-3 minutes.
Add the egg and vanilla extract, then beat until well combined and slightly bubbly, about 1 minute.
In a separate bowl, whisk together the flour, baking powder, and toasted almond slivers if using.
Gradually add the dry ingredients to the wet mixture, mixing just until a soft, slightly crumbly dough forms. If the dough feels too sticky, sprinkle in a little more flour and fold it in gently.
Chill the dough in the refrigerator for at least 30 minutes to help it relax and firm up, making it easier to shape.
Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for easy cleanup.
Once chilled, take small portions of the dough and roll them into finger-shaped logs, about 3 to 4 inches long, tapering slightly at one end to resemble a knuckle.
Place the shaped cookies on the prepared baking sheet, spacing them a couple of inches apart.
Use a toothpick or small knife to gently create creases and wrinkles on the skin, and add tiny nail marks at the knuckle tips for a realistic effect.
Bake in the preheated oven for about 15 minutes, or until the cookies are golden brown and slightly cracked on the surface.
Remove the cookies from the oven and let them cool for a few minutes on a wire rack until firm enough to handle but still delicate.
If desired, seal the nail marks with a tiny dab of icing or melted chocolate for extra creepy detail. Serve once cooled and enjoy their spooky, crumbly texture.
