• Preheat the oven to 320°F (160°C) and line a baking sheet with parchment paper.
• In a bowl, cream butter and powdered sugar until light and fluffy. Mix in vanilla extract and salt.
• Gradually add flour and mix until a smooth dough forms.
• Roll out dough between parchment paper to 1/8 inch thickness and cut into squares or rectangles. Place on the prepared baking sheet.
• Bake for 10-12 minutes or until the edges are lightly golden. Cool completely.

Cooling the Cookies:

• Once baked, the cookies should cool completely on a wire rack at room temperature. This takes about 15 minutes. Cooling ensures they firm up properly before assembly, as warm cookies may crumble or cause the chocolate to melt unevenly.

Setting the Chocolate (Optional Freezer Shortcut):

• After assembling the sandwiches with the chocolate filling, you can allow the chocolate to set naturally at room temperature, which takes about 10-15 minutes. However, if you're in a rush, place the assembled cookies in the freezer for about 5-7 minutes. This will firm up the chocolate quickly without affecting the cookies' crispness.
• Melt and temper the dark chocolate. Spread a thin layer of chocolate onto one cookie and press another on top to sandwich. Let set before serving.