Preparation

Make the semifreddo

• Line an 8-1/2×4-1/2-inch loaf pan with plastic wrap. In a 2-quart saucepan over medium heat, cook the sliced strawberries with 1/4 cup of the sugar, stirring occasionally, until the berries soften and begin to break apart, 5 to 7 minutes. Set aside.

  Choose a medium stainless-steel bowl that can rest just inside a medium saucepan. Pour about 1 inch of water in the saucepan and bring to a boil. Reduce the temperature to maintain a gentle simmer. Choose another bowl large enough to hold the medium bowl. Fill the large bowl with about 2 inches of ice water; set aside. Put the egg yolks, whole egg, and the remaining 1/4 cup sugar in the medium bowl and whisk until well combined and pale yellow, about 2 minutes. Add the reserved strawberry mixture and whisk to combine. Set the bowl over the saucepan without letting it touch the water and whisk constantly until the mixture is thick and leaves a trail when you lift the whisk, 3 to 4 minutes. Set the bowl in the ice water and whisk occasionally until cool, about 5 minutes.

  Meanwhile, in a large chilled metal mixing bowl with a hand mixer on medium-high speed (or in a stand mixer fitted with the whisk attachment), beat the cream to medium peaks, 2 to 3 minutes.

  Gently fold the whipped cream into the strawberry mixture until just combined. Pour the mixture into the loaf pan, smooth the surface, cover with plastic, and freeze for at least 6 hours and up to overnight.

Serve

• Toss the quartered strawberries with the sugar and Grand Marnier (if using) to taste. Let sit until the berries release some of their juices, 5 to 10 minutes.

  Meanwhile, remove the semifreddo from the freezer and let it sit at room temperature for 5 to 10 minutes to soften slightly. Invert onto a cutting board, remove the plastic, and slice. Serve topped with the quartered berries.