Soften butter at room temperature, then mix with sugar and salt.

Beat the egg in a separate bowl, then gradually add it to the butter mixture while stirring quickly to prevent separation. Add vanilla extract and mix well.

Add melted chocolate (using a double boiler) to the mixture and stir.

Add room-temperature milk and mix thoroughly.

Sift together all-purpose flour, cocoa powder, and baking powder, then fold into the mixture using a spatula.

Cover the dough with plastic wrap and refrigerate for 1 hour.

Divide the dough into 20g portions.

Roll each portion in sugar first, then coat with powdered sugar.

Place cookies on a baking tray with ample spacing.