Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the egg, cranberry sauce, and vanilla extract to the butter and sugar mixture. Mix until well combined.
In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, mixing until a soft dough forms.
Lightly flour your work surface and roll out the dough to about ¼ inch thick. Use the nail-shaped cookie cutter to cut out pieces and place them on the prepared baking sheet.
Bake in the preheated oven for 12-15 minutes, or until the edges are lightly golden. Allow the pieces to cool on a cooling rack.
In a small saucepan, combine the powdered sugar and milk to make a smooth glaze. Adjust the milk to get the desired consistency.
Drizzle the glaze over the cooled cranberry nails, and if desired, top with fresh cranberries for decoration.