Start with the custard so it has time to cool. In a saucepan, heat the milk until warm but not boiling.

In a separate bowl, whisk together egg yolks, sugar, and cornstarch until smooth. Slowly pour the warm milk into the mixture while whisking constantly.

Return everything to the saucepan and cook over medium heat, stirring continuously until thickened. Remove from heat, stir in butter and vanilla, then cover and chill.

In a mixing bowl, cream together butter and sugar until light and fluffy. Add the egg and vanilla extract, mixing until smooth.

In another bowl, combine flour, baking powder, and salt. Gradually add the dry ingredients to the wet mixture.

Add milk to create a soft, scoopable dough.

Preheat your oven to 180°C (350°F). Line baking trays with parchment paper.

Scoop small portions of dough and place them on the tray, leaving space between each.

Bake for 10–12 minutes or until the edges are lightly golden. Let cool completely.

Heat the heavy cream until just simmering, then pour it over the chopped chocolate. Let sit for a minute, then stir until smooth and glossy.

Once cookies are cooled, spoon or pipe custard onto one cookie and top with another, or simply add custard on top.

Drizzle or spread chocolate ganache over each cookie.

Let the ganache set slightly before serving.