In a saucepan, heat 2 cups of whole milk over medium heat until steaming. In a separate bowl, whisk together 4 egg yolks, ½ cup of granulated sugar, a pinch of salt, 1 tablespoon vanilla bean paste, and 2 tablespoons cornstarch until pale. Gradually mix the hot milk into the egg mixture, then return to heat and whisk continuously for 8-12 minutes until thickened. Stir in 2 tablespoons of unsalted butter, cover, and refrigerate until chilled.

Preheat your oven to 350°F (175°C). In a mixing bowl, whisk together 2½ cups of all-purpose flour, 1 teaspoon baking powder, and a pinch of salt. In another bowl, cream ½ cup unsalted butter and 1 cup granulated sugar until light and fluffy. Beat in 1 egg and 1 tablespoon vanilla bean paste until combined. Gradually add dry ingredients to form a soft dough.

Using a cookie scoop, portion out the dough into balls. Roll each ball in granulated sugar to coat and slightly flatten them with your hand. Place on a lined baking sheet.

Bake in the preheated oven for 9-10 minutes until edges are lightly golden. Allow to cool on the sheet for a few minutes, then transfer to wire racks to cool completely.

Pipe a generous dollop of chilled pastry cream onto the center of each cooled cookie. Sprinkle a thin layer of granulated sugar over the pastry cream and use a kitchen torch to caramelize the sugar until golden.

Serve immediately after assembly for the best texture.