Warm the milk in a saucepan until it's hot but not boiling. Keep it warm over low heat.
Mix together egg yolks, sugar, salt, vanilla, and cornstarch in a big bowl until smooth and light in color.
Slowly stir the warm milk into the mixture until it's well combined. Cook it in a saucepan until it thickens, stirring constantly.
Remove the creamy mixture from heat, stir in the butter, cover it directly with plastic wrap, and put it in the fridge until it's cold.
Preheat the oven to 350 degrees and line baking sheets with parchment paper.
Mix flour, baking powder, and salt in a bowl and set it aside.
Use an electric mixer or mix by hand to beat the butter and sugar until it's fluffy.
Add eggs and vanilla to the butter mixture, beat until it's light and fluffy.
Slowly add and mix in the dry ingredients until a dough forms.
Shape the dough into balls, coat them with sugar, place them on the baking sheets, gently flatten, and bake for 8-10 minutes.
Let the cookies cool on the baking sheet before transferring them to a cooling rack.
Put the chilled pastry cream into a piping bag with a small tip.
Once the cookies are cooled, pipe pastry cream on top of each.
Sprinkle sugar on the cream and use a kitchen blow torch to caramelize the sugar.
Let the cookies cool a bit after torching before serving.
