Step 1Line two baking sheets with Silpat or parchment paper and have a rubber spatula and cooking spray nearby. Heat the oven to 300 degrees.
Step 2In a medium saucepan over high heat, combine the hazelnuts, sugar and water. Cook, stirring constantly and vigorously to prevent the sugar from burning. After about 3 minutes the sugar will look granular in the pan. After this, it will become liquid and then it will begin to brown. Continue to cook the hazelnuts and sugar, stirring constantly, until the sugar is caramel colored, 7 to 10 minutes total.
Step 3Quickly turn the nuts out onto one of the prepared baking sheets. Working quickly before the sugar hardens, spray the spatula with the cooking spray and use it to gather the nuts into groupings of three, to form triangles. Place one of the remaining nuts on top of each triangle of nuts to create pyramids. If the sugar hardens too quickly, leave the remaining nuts on the sheet pan (remove the assembled clusters to the second pan) and place the pan in the oven until the sugar softens and is sticky, about 3 minutes, then continue.
Step 4When you're ready to dip the nuts in chocolate, pour the tempered chocolate into a medium bowl and have two dinner forks in front of you. Drop about 6 clusters of nuts into the bowl, not more than will fit in one layer. Use a fork to gently dip the nut clusters down into the chocolate to cover them. One at a time, pick up a nut cluster with one fork and tap it against the second fork to drain off enough of the excess chocolate that you can see the form of the nuts under the chocolate. Place the cluster on the second prepared baking sheet and repeat with the remaining hazelnut clusters. Allow the chocolate to cool on the Silpat. Transfer the cooled nut clusters to an airtight container and store them at room temperature for up to 1 week.