• Line a 9 x 5-inch loaf pan with plastic wrap, leaving enough overhang to cover the top of the semifreddo.

Whip the Cream:

• To prepare the whipped cream, use a chilled mixing bowl and whip 1 ½ cups of the cold heavy cream until soft peaks form.
• Cover and refrigerate until ready to use.

Make the Zabaglione:

• To make the zabaglione, grab a heatproof bowl and whisk together 4 egg yolks, ½ cup of the sugar, and 2 teaspoons of vanilla extract until well combined.
• Set the bowl over a pot of simmering hot water, making sure the bowl doesn’t touch the water, and whisk constantly until the mixture thickens, turns pale, and reaches 160°F, 7 to 10 minutes. Once done, take it off the heat.
• In a separate heatproof bowl, melt ½ cup of chocolate-hazelnut spread with ½ cup of chopped dark chocolate in the microwave (in 20-second intervals, stirring in between) or a double boiler until smooth and thoroughly combined.
• Slowly whisk the warm melted chocolate mixture into the warm zabaglione a little at a time until fully incorporated and smooth.
• Stir in ¼ cup of warmed heavy cream to help emulsify the chocolate mixture if the mixture becomes too thick or seizes. Stir until the mixture is smooth.
• Let the chocolate mixture cool to room temperature while you prepare the meringue.

Make the Meringue:

• In a clean mixing bowl, beat the egg whites with a pinch of salt until soft peaks form.
• Gradually add the remaining ¼ cup of sugar and continue to beat until glossy, stiff peaks form.

Assemble the Semifreddo:

• Gently fold the cooled chocolate mixture into your prepared whipped cream until well combined.
• Fold in the meringue until no lumps or white streaks remain.
• Fold in ¼ cup of chopped hazelnuts, taking care not to deflate the mixture.
• Carefully pour the mixture into the prepared loaf pan, smoothing the top.
• Fold the overhanging plastic wrap over the top to cover.
• Freeze for at least 6 hours or overnight for the best results.
• Before serving, unwrap the top of the semifreddo and invert it onto a serving platter.

Garnish the Dessert:

• Remove the plastic wrap and garnish with additional melted chocolate-hazelnut spread and sprinkle over ¾ cup of chopped hazelnuts.
• Cut into slices to serve.