Shortbread dough

1. In a large mixing bowl, cream the softened butter with the powdered sugar with an electric mixer on medium speed for about 2-3 minutes until creamy.
2. Add the egg and vanilla extract and beat again for a good minute to incorporate.
3. Finish with the dry ingredients, flour, salt and baking powder (optional) and mix again with an electric mixer just until incorporated and smooth.
4. Gather the dough with your hands to form a homogeneous dough ball and cover it with plastic wrap, then place it in the refrigerator for about 3o minutes.
5. Roll out the dough on a floured surface with a rolling pin to a thickness of 3-4 mm (or between 2 sheets of baking paper).
6. If necessary, place the dough in the freezer for 10-15 minutes before cutting out pieces of cookies using the special linzer cookie cutter. (cut out 1 full cookie and 1 cookie with a hole to make a sandwich cookie).
7. Place the shortbread dough pieces on a baking sheet lined with baking paper and let it rest in the freezer for 30 minutes.
   
   

Baking

1. Preheat the oven to 340°F / 170°C and bake the cookies in the oven at half height for about 10 minutes, making sure to space them about 5 cm apart as they will puff up a bit (especially if you use baking powder).
2. The shortbread cookies are ready when they are lightly browned on the edges, be careful not to overcook them or they will be too dry, they should still be a little soft in the center, they will firm up as they cool.
   Take the shortbread out of the oven and let it cool down a bit before moving it to a cooling rack or a large dish.

Filling

1. Place the chocolate spread in a small piping bag and pipe a small amount of Nutella onto the center of a full cookie.
2. Form a sandwich by placing a second shortbread with a hole in the center on top and press lightly to spread the filling.
3. Place the shortbread in the fridge for 20 minutes to firm up the filling if needed and enjoy