1. 1. Preheat your oven to 350°F (175°C). Grease or line a baking sheet with parchment paper.
   2. In a large mixing bowl, cream together the butter and powdered sugar until light and fluffy.
   3. Beat in the egg and vanilla extract until fully combined.
   4. Gradually add in the flour and salt, mixing until a smooth dough forms.
   5. Roll the dough into 1-inch balls and place them on the prepared baking sheet.
   6. Using your fingers or a small tool, gently press each ball into an oval shape. (Alternatively, you can roll the dough thin and cut into strips to wrap around the ends of clothespins.)
   7. Bake the cookies in the preheated oven for 8-10 minutes, or until they are golden brown on the edges.
   8. Remove from the oven and allow them to cool completely.

For the Filling:

1. 1. 1. In a mixing bowl, beat together the powdered sugar, butter, vanilla extract, milk, and salt until smooth and creamy.

      2. Once the cookies have cooled, spread the filling between two cookies, pressing them together gently.

      3. Repeat with the remaining cookies. Serve and enjoy!