In a saucepan over medium heat, warm whole milk until steaming. In a bowl, whisk egg yolks, granulated sugar, salt, vanilla bean paste, and cornstarch. Gradually pour hot milk into egg mixture while whisking, then return to saucepan and cook until thickened, about 5-7 minutes. Chill in refrigerator.

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

In a bowl, whisk together all-purpose flour, baking powder, and salt. Set aside.

In a mixing bowl, cream together softened butter and granulated sugar until light and fluffy. Incorporate egg and vanilla bean paste until smooth.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until a soft, slightly sticky dough forms.

Roll dough into 1½-inch balls and coat in granulated sugar. Flatten slightly and place on prepared cookie sheets.

Bake for 9-10 minutes until edges are golden, allowing centers to remain soft. Cool on sheets for 5 minutes.

Pipe chilled pastry cream onto cookies, sprinkle sugar over cream, and use a kitchen torch to caramelize the sugar until golden brown.