Line a 9x5 loaf pan with plastic wrap, leaving 3-4 inches overhanging on all edges.

Place mixer bowl and whisk attachment in the freezer to chill for 30 minutes.

Place heavy cream, 3 tablespoons of sugar, and 1 teaspoon of vanilla in mixer bowl and whip on high until stiff peaks form. Transfer whipped cream to a large bowl and refrigerate.

Put about an inch of water in a saucepan that will hold your mixer bowl as a double boiler. Bring water to a simmer over medium heat.

Clean bowl and whisk attachment thoroughly. Using a hand whisk, whisk together egg whites and 3 tablespoons of sugar in the mixing bowl and place over simmering water. Whisking continuously, cook until sugar is dissolved and mixture is opaque (165°F). Transfer bowl to mixer fitted with the whisk attachment and whip until stiff peaks form, about 2 minutes. Add 1 teaspoon vanilla and incorporate. Transfer egg white mixture to a bowl, and refrigerate until needed.

Clean bowl, whisk, and whisk attachment thoroughly.

In the mixer bowl, whisk together egg yolks, remaining sugar, and 1 teaspoon vanilla. Place over simmering water and cook, whisking continuously, until thick and pale yellow (165°F). Transfer bowl to mixer fitted with the whisk attachment and whip on high until doubled in volume, about 3 minutes.

Fold egg yolk mixture into whipped cream. In three additions, fold in whipped egg whites. Transfer to prepared loaf pan, fold over plastic wrap, and freeze for at least 8 hours.

To serve, unwrap and slice.