Method
1. Add egg yolk and granulated sugar to a clean large mixing bowl
2. Whisk until pale and light - approx 3 min
3. Add unsalted butter
4. Beat until well combined
5. Add cornstarch and baking powder to a clean small bowl
6. Mix in dry ingredients to dough gradually while mixing
7. Wrap with plastic wrap
8. Chill in fridge - 30 min
9. Pre-heat oven - 175°C / 350°F
10. Line 2 clean baking sheets with parchment paper
11. Sprinkle with cornstarch
12. Roll out until 1/8" (5mm) thick
13. Cut
14. Transfer dough to 2 baking sheets
15. Bake until browned at edges - 6 min, 175°C / 350°F
16. Transfer carefully onto cooling rack
17. Assemble dulce de leche with the cookies gently
18. Dust with powdered sugar