01 - 
                Turn your oven on to 350°F (175°C). Line your baking trays with parchment paper to stop sticking.
              
              
              
                02 - 
                Grab a mixing bowl and an electric hand mixer. Beat the butter together with sugar until the mixture turns fluffy and white. Add in the vanilla and blend it all together.
              
              
              
                03 - 
                Take another bowl and sift the flour, cocoa powder, and salt together to combine them evenly.
              
              
              
                04 - 
                Slowly pour your dry mixture into your butter mix. Stir and work it in until the dough feels smooth and can hold its shape.
              
              
              
                05 - 
                Form the dough into balls about 1 inch (2.5 cm) wide. Cover each ball in the chopped hazelnuts. Lay them out on your baking trays and leave 2-inch (5 cm) gaps between each cookie.
              
              
              
                06 - 
                Use a small spoon or your thumb to gently press a little dent into the middle of each dough ball.
              
              
              
                07 - 
                Pop the trays into the hot oven. Bake everything for about 12 to 14 minutes, until they're firm but still soft to the touch.
              
              
              
                08 - 
                Remove the cookies from the oven. While they're warm, press the centers again if needed. Drop a teaspoon of the hazelnut spread into each dent. Decorate with a whole hazelnut, if you'd like.
              
              
              
                09 - 
                Let the cookies sit on the tray to cool for around 5 minutes. After that, move them to a rack to finish cooling completely.