Preheat the oven to 100°C. Line 2 baking sheets with parchment paper.
Chop the hazelnuts in a food processor. Be careful not to over grind them or the oil will come out.
Beat the egg whites until soft peaks form. Add half of the sugar and whip again until thick and shiny. Beat in the remaining sugar, little by little.
Drop 24 spoonfuls onto the parchment paper with a teaspoon. Put in the oven until the meringues become crisp, which should take about an hour. Gently move them to a wire rack and allow them to cool down.
Put the chocolate into a heatproof bowl and melt in a bain-marie.
Dunk the bottom of each meringue in the melted chocolate then in the chopped hazelnuts. Let them harden on the cooling rack.
Whip the cream and icing sugar until it thickens. Spread over the chocolate side of each meringue and sandwich them together in pairs.