Line an 8½x4½-inch metal loaf pan with plastic wrap, letting excess extend 2 inches over all sides of pan. Freeze until ready to use or for at least 30 minutes.

In a large bowl, beat cold cream, vanilla, and salt with a hand mixer at medium-high speed until stiff peaks form, 3 to 4 minutes. Refrigerate until ready to use.

In a heatproof bowl, whisk together eggs and sugar. Place bowl over a saucepan of simmering water. Cook, whisking frequently, until sugar is melted and an instant-read thermometer registers at least 160°F (71°C). Remove from heat. Beat egg mixture with a hand mixer at medium-high speed until mixture has cooled down and tripled in volume and has a thick and ribbonlike consistency, about 5 minutes.

Add egg mixture to whipped cream mixture, and gently fold until combined and no streaks remain. Spoon into prepared pan, smoothing top with an offset spatula. Cover with excess plastic wrap, and freeze until firm, at least 5 hours, preferably overnight.

Let semifreddo stand at room temperature for 5 minutes to soften slightly. Using excess plastic wrap as handles, remove from pan, and slice as desired. Freeze in an airtight container for up to 2 weeks.