Using a chef knife, finely chop half of the hazelnuts; set aside.

In a medium-sized saucepan, bring an inch of water to a simmer.

Meanwhile, in a large bowl, combine the chocolate, sugar, egg white, vanilla and 2 tablespoons of water.

Set the bowl over the simmering water and stir with a rubber spatula until the chocolate is melted and the sugar is completely dissolved, about 5 minutes.

Remove from the heat and stir in the whole and chopped hazelnuts and stir to combine.

Refrigerate the mixture, uncovered, for 1 hour.

Using a bowl scraper, dump the mixture onto a large sheet of plastic wrap.

Use the plastic wrap to shape the chocolate into a log 9 ½-inches in length; refrigerate for 1 hour.

Transfer the log to a fresh sheet of plastic wrap and sprinkle the confectioners sugar on top. Roll to coat the log in the sugar, pressing it onto the sides; refrigerate for 1 hour, up to overnight.

To serve, shake off excess sugar and slice ¼-inch medallions.