Add the room temperature butter, powdered sugar, vanilla, and milk to an electric mixer on medium speed. Mix together until smooth.
Sift the flour and slowly add it to the mixer with the salt on a very low speed.
Scoop the dough out of the mixer and place it onto a floured surface. Roll out the dough with a rolling pin until 3/4 a cm thick.
Use the biscuit cutter to cut out an even amount, but add in the extra cutout for the other half.
Transfer to a non-stick or parchment lined baking sheet
Bake 6 to 7 minutes. Do not let them brown and allow them to sit on the pan for about five minutes before transferring them to the cooling rack.
Once the cookies are completely cooled, add two tsps of caramel sauce to the center of the bottom cookie (but leave 3/4 cm around the edges uncovered or it'll pour over) and add the cutout cookie layer on top.Sprinkle with powdered sugar or sugar crystals