1. Preheat the oven to 300°F (150°C) and line a baking sheet with parchment paper.

2. In a medium bowl, whisk the sugar and egg yolk together until they are pale and fluffy.

3. Add the softened butter to the bowl and whisk until the mixture is smooth and creamy.

4. Gradually add the flour to the bowl, whisking continuously until a dough forms.

5. Turn the dough out onto a floured surface and knead for about 5 minutes, until it is smooth and pliable.

6. Divide the dough into 18 equal pieces and shape each one into a crown.

7. Place the crowns on the prepared baking sheet, leaving about 1 inch (2.5 cm) of space between each one.

8. Dust the tops with meringue powder and bake for 18-20 minutes, or until they are lightly golden.

9. Remove the crowns from the oven and let them cool completely on a wire rack.

10. Dust with confectioners sugar before serving.