Once the shortbread is baked, you can start on your caramel.
In a small saucepan, warm the cream and the salt over low heat and stir constantly until warm - should not be boiling.
Once ready put on the side.
In a large saucepan, dissolve the sugar and glucose with the water, on medium-high heat until the sugar dissolves. Cook for 5-10 minutes, until the liquid turns golden-dark. You can choose to stop it at golden.
Once ready and while still hot, slowly pour the contents of the large pan into the slow pan - it will bubble and sizzle, which is normal.
Stir the mixture in only once the bubbles have stopped, and add the butter in.
Stir in well and add the hazelnuts in.
Pour instantly on the shortbread, and level up with the help of a spatula.
Let it rest in the freezer for about 15-20 minutes.