Combine the butter and sugar powder in a mixing bowl and whisk until soft and creamy.
Add vanilla essence and salt and combine well.
Add flour and mix well until everything is well combined.
Knead the mixture to make it into a soft dough.
Wrap the prepared dough in a plastic wrap and refrigerate for about 40 – 60 minutes.
Preheat oven to 180 degree C. Line the baking tray with parchment paper and set aside.
Remove the dough from the refrigerator. Dust the work surface with flour and roll out the dough into 1/4 inch thick circle.
If the dough is very stiff to be rolled, let it sit at room temperature for few minutes.
Cut the cookies with a cookie cutter and press one side of the cookies against the brown sugar.
place them on the prepared baking tray. Re-roll the scraps and repeat.
Bake them in the preheated oven at 180 degree C for about 10 – 15 minutes or until lightly browned on edges.
Remove from the oven and let them cool for a couple of minutes.
Remove the cookies from the tray and let them cool completely on a wire rack.
Once cool, place some nutella on one cookie and place another cookie on top to make a sandwich cookie.