Place a heavy cutting board on the edge of your counter near your stove. This will hold skewered hazelnuts in place after dipping in sugar. Place a baking sheet lined with parchment on the floor. This will catch sugar drips and make clean-up easier.
Heat sugar and water in a small saucepan over medium-high heat. Heat sugar, brushing down crystals from the sides of the pan with a wet brush, until mixture is golden. Do not stir.
Meanwhile, skewer hazelnuts gently on one end with wooden skewers. Insert skewer enough to hold hazelnut but not break it.
Remove caramel from heat once it's golden. Allow to cool slightly and thicken. This will help it coat the hazelnut.
Dip hazelnut in caramel to coat. Place skewer under heavy cutting board and allow sugar to drip and cool. Repeat with remaining skewered hazelnuts and caramel. If caramel gets too thick, reheat a bit to desired consistency.
Allow nuts to cool completely. Cut caramel strands to desired length. Remove nuts and top tart with caramelized hazelnuts.