Beat the softened butter and 40 g powdered sugar for about 3 minutes, until creamy.

Add the lime zest, lime juice, vanilla, and fleur de sel. Mix until combined.

Whisk together the flour and cornstarch.

Add the dry ingredients to the butter mixture and mix just until a soft dough forms.

Shape the dough into a log about 1 1/2 inches (4 cm) in diameter.

Wrap tightly and refrigerate for 1 hour, or until firm.

Preheat the oven to 300°F (150°C) fan/convection and line a baking sheet with parchment.

Slice the chilled log into rounds approximately 1/3 inch (8 mm) thick.

Arrange on the prepared baking sheet.

Bake for about 18 minutes, until set and only lightly golden.

Let the cookies cool.

Coat each cookie generously in the remaining 80 g powdered sugar.