In a saucepan, heat the whole milk over medium heat until warm.

In a mixing bowl, whisk together the egg yolks and sugar until well combined.

Gradually pour the warm milk into the egg mixture while whisking continuously.

Stir in the salt, vanilla bean paste, and lemon zest.

In a separate bowl, whisk together the cornstarch, all-purpose flour, baking powder, baking soda, and salt.

Slowly add the dry ingredients to the wet mixture and mix until a dough forms.

Fold in the unsalted butter cubes until fully incorporated.

Refrigerate the dough for at least 30 minutes.

Preheat the oven to 350°F (175°C).

Roll the dough into balls and place them on a baking sheet lined with parchment paper.

Bake for 10 minutes or until lightly golden.

Allow the cookies to cool.

In a small bowl, mix granulated sugar with lemon zest for the topping.

Sprinkle the lemon sugar evenly over cooled cookies and use a kitchen torch to brûlée the sugar until caramelized.