Heat 2 cups of whole milk in a saucepan over medium heat until it steams. In a mixing bowl, whisk together 4 egg yolks, ½ cup of granulated sugar, a pinch of salt, 2 teaspoons of vanilla bean paste, and 2 tablespoons of cornstarch until pale and thick. Gradually whisk in the warm milk, return to saucepan, and cook over medium-low heat for 8-12 minutes, stirring continuously until thickened. Remove from heat, blend in 2 tablespoons of unsalted butter, cover and cool completely.

Preheat oven to 350°F (177°C). In a bowl, whisk 2 cups of all-purpose flour, 1 teaspoon of baking powder, and a pinch of salt. In another bowl, cream together ½ cup of unsalted butter and 1 cup of granulated sugar until fluffy. Mix in 1 egg and 2 teaspoons of vanilla bean paste. Gradually fold in dry ingredients forming a soft dough.

Scoop cookie dough and roll each ball in granulated sugar. Place on parchment-lined baking sheet, ensuring 2 inches apart. Bake for 9-10 minutes until edges are golden and centers are soft. Cool on baking sheet for a few minutes before transferring to wire racks.

Once cooled, pipe cooled pastry cream onto each cookie, creating a mound. Sprinkle a thin layer of granulated sugar on top and caramelize with a kitchen torch until golden and crunchy. Allow to cool slightly before serving.