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

In a large bowl, whisk together your dry ingredients – flour, baking powder, baking soda, and salt.

Using an electric mixer, cream the butter, granulated sugar, and brown sugar until light and fluffy (about 2-3 minutes).

Add eggs and vanilla extract to the butter mixture and beat until combined.

Gradually add your dry ingredients to the wet mixture, mixing until a soft dough forms.

Scoop out small portions of dough (about 1-2 tablespoons) and roll into balls.

Place them on the baking sheet, leaving space for spreading.

Bake for 10-12 minutes, or until the edges turn golden. Allow cookies to cool completely on a cooling rack.

Heat milk in a saucepan until it begins to steam but doesn’t boil.

Whisk together egg yolks, sugar, and cornstarch in a separate bowl.

Gradually pour the warm milk into the egg mixture, whisking constantly to prevent curdling.

Return the mixture to the saucepan, cooking on medium heat while stirring until thickened.

Stir in vanilla extract and cool the custard completely.

Heat heavy cream in a small saucepan until steaming, then pour over the chocolate chips in a heatproof bowl.

Stir until the chocolate melts and mixture becomes smooth and glossy.

Pipe or spoon a dollop of custard filling onto the flat side of a cookie.

Sandwich another cookie on top and gently press to spread the filling.

Drizzle or dip the top of the cookie sandwich into the chocolate glaze.

Allow the glaze to set before serving.