Beat butter and sugar at medium speed with a stand mixer until combined and creamy, about 1 minute.

Add eggs one at a time, then vanilla extract, beating until combined and scraping the sides as needed.

In a separate bowl, whisk together flour, baking powder, and salt.

Add flour mixture to the butter mixture alternately with milk, beating at low speed until combined.

Divide dough in half, shape into disks, wrap in plastic wrap, and chill for 4 hours or overnight.

Melt butter and chopped chocolate in a microwave-safe bowl, stirring every 20 seconds until smooth.

Stir sugar, vanilla, and salt into the chocolate mixture until combined; add egg and flour for the filling.

Chill filling for 30 minutes.

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

Roll out dough to 1/8 inch thick, cut into 3-inch circles, and add 1 teaspoon filling to the center.

Shape the dough edges into triangles around the filling, ensuring the sides overlap and press firmly.

Chill shaped cookies in the freezer for 10 minutes or fridge for 30 minutes.

Bake in batches on the middle rack for 12 to 14 minutes until lightly browned.