In a large mixing bowl, cream together 226 g of softened unsalted butter, 140 g of confectioner’s sugar, and 1 teaspoon of sea salt using an electric mixer until light and fluffy, about 3-5 minutes.

Add 4 egg yolks and 5 mL of vanilla extract to the creamed mixture, beating until well combined.

Divide the cookie mixture into bowls to incorporate colors, mixing in matcha powder, purple sweet potato powder, or cocoa powder as desired.

In a separate bowl, whisk together 454 g of all-purpose flour and ¼ teaspoon of baking powder before integrating this into the wet ingredients.

Gradually add the dry mixtures to the butter mixture, mixing on low speed until a soft dough forms.

Shape the dough into discs, wrap in plastic wrap, and chill in the refrigerator for about 30 minutes.

Scoop tablespoons of dough, roll them into finger shapes, and press a whole blanched almond into the end for the 'nail'.

Transfer shaped cookies to a lined baking tray and freeze for 1 hour.

Preheat the oven to 325°F (163°C) and bake the frozen cookies for 20-25 minutes until lightly golden.

Once cooled, gently remove the almond 'nails', fill indentations with jam or melted chocolate, and replace the almond.