Preheat oven to 350F. Toast hazelnuts for 10 minutes. Let cool, then grind in a food processor until nuts have the consistency of sand.
In a double boiler or heavy bottomed pot, heat cream and chocolate over low heat. Stir frequently until chocolate is completely melted. Add hazelnuts and stir to combine. Remove from heat and transfer to refrigerator to cool.
While the chocolate is cooling, whisk together egg whites in an electric mixer until stiff peaks form.
Next, heat sugar and water in a small saucepan, stirring until sugar dissolves. Bring sugar syrup up to 250F degrees, then, pour down the side of the bowl with the egg whites and continue to whisk on high speed until mixture forms stiff peaks again. The bowl should be cool to the touch and the mixture should be thick and fluffy. This will take between 6-10 minutes.
Once meringue is complete, transfer to a large bowl. Pour cooled chocolate cream mixture into mixer and whisk until fluffy, about 5-10 minutes. Fold chocolate into meringue until fully mixed.
Cover a 9 inch loaf tin with plastic wrap. Pour mixture into tin and smooth with spatula. Freeze for at least 3 hours, until semifreddo has hardened.
Remove from freezer, let sit for 5-10 minutes, then flip onto plate. Top with chopped hazelnuts and raspberries and slice into ½ inch thick pieces. Serve immediately.
Recipe by Things I Made Today at https://www.thingsimadetoday.com/2014/12/10/chocolate-hazelnut-semifreddo-stats-28/