Heat 2 cups of whole milk in a saucepan over medium heat until steaming, without boiling. In a separate bowl, whisk together egg yolks, granulated sugar, salt, vanilla bean paste, and cornstarch until smooth. Gradually whisk in the hot milk, return to saucepan, and cook on low heat until thickened, about 5-7 minutes. Chill after transferring to a bowl.

In a bowl, whisk together all-purpose flour, baking powder, and salt until combined. In a large bowl, cream together unsalted butter and granulated sugar until light and fluffy. Add an egg and remaining vanilla bean paste, and mix until incorporated. Gradually combine with dry ingredients to form a dough.

Preheat oven to 350°F (175°C) and line baking sheets with parchment paper. Scoop chilled dough into balls, roll in sugar, and flatten slightly. Bake for 9-10 minutes until edges are golden and centers are soft. Cool on baking sheets before transferring to a wire rack.

Pipe pastry cream onto the center of cooled cookies and sprinkle granulated sugar on top. Use a torch to caramelize the sugar until golden and crunchy.