In a medium saucepan, heat 2 cups of whole milk over medium heat until steaming, but do not let it boil. In a separate bowl, whisk together 4 egg yolks, ½ cup granulated sugar, a pinch of salt, 1 tablespoon vanilla bean paste, and 2 tablespoons cornstarch until smooth. Gradually whisk the egg mixture into the hot milk, stirring continuously for 8-12 minutes until thickened. Remove from heat, stir in 2 tablespoons of butter, and cool it in the refrigerator.

In a mixing bowl, whisk together 2½ cups of all-purpose flour, 1 teaspoon baking powder, and ½ teaspoon salt until well blended. In another large bowl, cream together 1 cup of unsalted butter and 1 cup of granulated sugar for 3-5 minutes until light and fluffy. Beat in 1 large egg and 1 tablespoon of vanilla bean paste until fully incorporated, then gradually add the dry ingredients to form a soft dough.

Preheat your oven to 350°F (175°C). Use a cookie scoop to portion out the dough and roll it into balls. Next, roll each ball in ½ cup of granulated sugar to coat it evenly. On a lined baking sheet, flatten each dough ball to about ½ inch thick with the palm of your hand.

Place the baking sheet in the preheated oven and bake for 9-10 minutes. Keep an eye on them; the edges should turn golden brown, while the centers remain soft and slightly puffed. Once baked, remove from the oven and let the cookies cool on the sheet for about 5 minutes before transferring them to a wire rack to cool completely.

Once the cookies have cooled, carefully pipe the chilled pastry cream onto the center of each cookie using a piping bag. Leave the edges of the cookies clean for the final touches.

Sprinkle a thin layer of granulated sugar over the pastry cream on each cookie. Using a kitchen torch, caramelize the sugar until it melts and turns a beautiful golden brown.

Allow the caramelized sugar tops to cool and harden slightly before serving. Store leftovers in an airtight container in the refrigerator for up to 2 days.