Line a baking sheet with parchment paper and set it aside.

Mix sugar, ground cinnamon, and salt in a small bowl. In a large frying pan, pour water and sugar mixture and mix with a wooden spatula. Bring the pan over medium-high heat. Once the sugar starts to boil and large bubbles form, add whole hazelnuts.

Immediately, low the heat to medium, and continue to stir continuously. The sugar syrup will start to crystallize, coating the nuts thoroughly.

Extra tip: Medium heat and constant stirring help the sugar coat the nuts. If you stop, the sugar will solidify, and the nuts won't be coated.

Continue stirring until the sugar stops adhering to hazelnuts; the nuts will be covered with sugar.

Transfer hazelnuts to a working surface, marble slab, or prepared baking sheet lined with parchment paper and allow to cool down. If any nuts are stuck together, separate them with the wooden spatula while they are warm.

Collect the sugar-coated hazelnuts, and place them in an airtight container or a mason jar. Discard the remaining sugar left on the sheet.