Grease a 5-by-9-inch loaf pan. Line the pan with plastic wrap, letting the wrap hang over the short ends by about 1 inch. Freeze until ready to use. Using an electric mixer, whip the cream until soft peaks form; cover and refrigerate.
In a double boiler, using a handheld mixer, beat the eggs and sugar at high speed off the heat until fluffy, about 5 minutes. Place over simmering water and beat at high speed until almost doubled in volume, about 8 minutes; transfer to a large bowl.
In a small bowl, microwave the chocolate-hazelnut spread until melted, about 30 seconds. Stir into the egg mixture until almost blended. Let cool for about 20 minutes. Fold in the nuts; then, working in 3 batches, fold in the whipped cream. Pour the mixture into the prepared pan. Cover with plastic wrap and freeze for 6 hours or overnight. Using the plastic overhang as handles, lift the semifreddo from the pan. Cut into 1-inch slices and serve immediately.
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