Steps
1. Preheat the oven to 175°C (350°F).
2. In a bowl, mix the flour and powdered sugar.
3. Add the cold butter cubes and rub into the flour mixture until it resembles coarse crumbs.
4. Stir in the egg yolk and vanilla extract, knead gently until a dough forms.
5. Roll the dough out to about 4mm thickness on a floured surface.
6. Using a small surfboard-shaped cookie cutter, cut out cookies and place them on a baking sheet lined with parchment paper.
7. Bake for 10-12 minutes or until lightly golden at the edges.
8. Allow cookies to cool completely.
9. Prepare royal icing in blue, white, and pink colors.
10. Use the blue and white icing to create waves and surfboard patterns on the cookies.
11. Carefully place small edible Hawaiian flowers on top of the wet icing as decorations.
12. Add sugar seashells and starfish around or on the cookies while the icing is still wet to adhere.
13. Let the icing dry completely before serving.