Line a 9x5-inch metal loaf pan (about 3 inches high) with 2 sheets of parchment paper, positioning them perpendicular to each other, so that the parchment hangs about 2 inches over all 4 sides of the pan to form a sling. Place in the freezer.

Place 1 ¼ cups cold heavy cream and 1 tablespoon vanilla extract in the bowl of a stand mixer (or medium bowl if using an electric hand mixer). Beat with the whisk attachment on high speed until stiff peaks form, 2 to 4 minutes. If using a stand mixer, transfer the whipped cream to another bowl, cover, and refrigerate. Wipe out the stand mixer bowl, and rinse and dry the whisk attachment. (If using an electric hand mixer, just cover and refrigerate.)

Fill a medium saucepan with about 1 ½ inches water, making sure that the stand mixer or large heatproof bowl can sit on top without touching the water. Bring to a simmer over medium heat.

Place 4 large eggs, ¾ cup granulated sugar, and ¼ teaspoon kosher salt in the bowl and whisk to combine. Set over the simmering water and cook, whisking constantly, until the sugar dissolves, the mixture is lightened in color and foamy, and it registers 165°F on an instant-read thermometer, 2 to 3 minutes.

Remove the bowl from the heat. Beat with the whisk attachment on high speed until the bowl is cool to the touch and the egg mixture is thickened, glossy, and pale yellow in color, 7 to 10 minutes.

Add the whipped cream and fold it in with a flexible spatula until fully incorporated and no streaks remain. Transfer to the loaf pan and smooth out the top. Cover with the excess parchment paper, pressing it gently against the surface, then wrap the pan tightly with plastic wrap. Freeze until solid, at least 8 hours or preferably overnight (and up to 3 days).

When ready to serve, unwrap and uncover the semifreddo. Invert the semifreddo onto a serving platter and remove the parchment. Top with strawberry glaze or raspberry sauce and fresh raspberries if desired. Slice crosswise into 1-inch-thick slices.