Prepare a 9"-5" loaf pan by placing parchment paper in the bottom of the pan and a strip of parchment paper around the edges of the pan. Set aside
Add the egg yolks, sugar, lemon juice, lemon zest and salt to a small saucepan. Heat over medium low heat, whisking constantly until the mix begins to thicken. If you have a candy thermometer, place it in the mix as it cooks and stop when it reached 170 degrees F (this should take about 4 minutes).
Remove the curd from the heat and stir in the vanilla extract. Strain through a fine mesh sieve and then add the curd to the bowl of an electric mixer. Beat the curd until cooled and very fluffy.
In a separate bowl, whip the heavy cream until stiff peaks form.
Fold the cooled curd into the whipped cream gently.
Pour the lemon cream into the prepared cake pan and smooth the top.
Sprinkle the top with the sliced almonds, pressing them gently onto the surface (this will be the semifreddo “crust”).
Wrap the loaf pan completely with plastic wrap and freeze for at least 8 hours, overnight if possible.
Once frozen, remove from the freezer, take out the plastic wrap and run a sharp knife around the edge of the loaf pan between the parchment and the pan. Flip the dessert onto a serving tray or plate.