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

In a large bowl, cream the butter and sugar together until light and fluffy.

Add the eggs and vanilla extract and mix until fully combined.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing just until a smooth dough forms.

Scoop tablespoon-sized portions of dough onto the prepared baking sheets, leaving space between each one.

Bake for 10–12 minutes, or until the edges are lightly golden. The cookies should stay pale and soft in the center.

Let the cookies cool completely before filling them.

In a saucepan, whisk together the milk, sugar, cornstarch, and salt over medium heat. Cook while stirring constantly until thickened.

In a small bowl, whisk the egg yolks. Slowly add a little of the hot milk mixture to the yolks to temper them.

Return everything to the saucepan and cook for 1–2 more minutes until smooth and glossy.

Remove from heat and stir in the vanilla extract.

Cover the surface directly with plastic wrap and refrigerate until completely chilled.

Heat the heavy cream until steaming but not boiling.

Pour it over the chocolate chips and let sit for 1 minute. Then stir until smooth and glossy.

Set aside to cool slightly before using.

Take half of the cookies and spread or pipe the cream filling onto their flat sides.

Top with the remaining cookies to form sandwiches.

Spoon or drizzle the chocolate ganache over the tops, allowing it to gently drip.

Allow the chocolate to set before serving.