In a saucepan over medium heat, warm whole milk until steaming but not boiling, about 5 minutes.

In a bowl, whisk together egg yolks, granulated sugar, salt, vanilla bean paste, and cornstarch until pale and smooth, about 2 minutes.

Gradually add warm milk to the egg mixture while whisking continuously.

Return the mixture to the saucepan and cook over medium-low heat for 8-12 minutes, stirring constantly until it thickens.

Remove from heat, stir in unsalted butter until melted, cover with plastic wrap, and refrigerate until fully chilled.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

In a medium bowl, whisk together flour, baking powder, and a pinch of salt.

In a large mixing bowl, cream together softened butter and granulated sugar using a hand mixer until fluffy, about 3-4 minutes.

Add in one egg and mix until light and pale, then gradually incorporate the dry ingredients to form a cohesive dough.

Roll the dough into balls, about 1-2 inches in diameter, then roll in sugar to coat and place on prepared sheets.

Flatten each ball gently to form disks about ½ inch thick.

Bake the cookies for 9-10 minutes, looking for a light golden color around the edges.

Cool cookies on the sheets for about 5 minutes, then transfer to a wire rack to cool completely.

Pipe chilled vanilla pastry cream onto each cookie generously.

Sprinkle a thin layer of granulated sugar on top of the cream, then caramelize with a kitchen torch until golden brown.

Let the cookies cool for an additional 10 minutes after caramelizing the sugar.