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1
MAKE THE BASE:
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2
Preheat the oven to 350u00b0F with rack in middle. Spread the hazelnuts out on a rimmed baking sheet and bake until fragrantly toasty and the inside of the nuts are golden, 10 to 15 minutes. Immediately wrap the nuts in a clean kitchen towel and let them stand 3 minutes, then rub the nuts vigorously in the towel to remove as much of the skins as possible. Let the nuts cool completely.
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3
In a food processor grind the nuts with the sugar and the salt, pulsing, until they are finely ground. Add the butter and pulse until it is incorporated. Press the nut mixture in an even layer on the bottom of the springform pan.
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4
MAKE THE SEMIFREDDO:
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5
In a metal bowl set over a saucepan of barely simmering water melt the chocolate, stirring occasionally, until smooth. Remove the bowl from the pan.
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6
In a large bowl with an electric mixer at medium-high speed beat the whites with the salt until they hold soft peaks. Add 1/3 cup sugar a little at a time, beating, and continue beating until the meringue just holds stiff glossy peaks. Transfer the meringue to another bowl.
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7
In the same large bowl with the electric mixer (no need to clean the bowl or the beaters) beat the cream with the remaining 3 tablespoons sugar until it just holds stiff peaks. Stir one-fourth of the meringue into the cream, then fold in the remaining whites. Fold in the chocolate, then fold in two-thirds of the chopped Baci.
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8
Transfer the chocolate filling to the pan, spreading the top evenly, then sprinkle the remaining chopped Baci evenly over the top, pressing it in gently.
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9
Cover the pan tightly with plastic wrap and freeze the semifreddo until firm, at least 5 hours. Let the semifreddo stand at room temperature to soften slightly, about 20 minutes, before slicing into wedges and serving.
