Line a 9x5-inch (23x12.5cm) loaf pan with plastic wrap, leaving some extra hanging off the sides.

Set up a small bowl with a fine mesh strainer on top of it over a large bowl of ice and place all this near the stove.

In a small saucepan over low heat, whisk the egg yolks, lemon juice, sugar, lemon zest, and salt.

Stir constantly until the mixture begins to thicken and coat the back of a spoon.

Immediately pour the curd through the prepared strainer to stop the cooking. Stir in the vanilla extract and let the curd cool completely, stirring occasionally to speed the cooling.

Once the curd is cold, whip the cream to soft peaks in a large bowl.

Gently fold the curd into the whipped cream until evenly mixed and then spread into the prepared loaf pan. Cover the semifreddo with the extra plastic wrap and freeze for at least 8 hours (or overnight).

When ready to serve, remove from the pan, unwrap and serve slices with some fresh berries. Store any leftovers well wrapped in the freezer for up to 2 weeks.