Prepare a double boiler or fit a heatproof bowl over a small saucepan of simmering water. In the bowl, combine the egg yolks and 1/2 cup of sugar, and whisk until frothy. Transfer the bowl immediately to an ice bath, stirring occasionally, until cool.
Meanwhile, in a separate bowl, whip the heavy cream to medium peaks. Fold the whipped cream into the cooled egg yolk mixture and then stir in the cinnamon.
In a separate mixing bowl, whip the egg whites and amaretto liqueur until soft peaks form and fold that into the egg yolk-cream mixture. Pour the mixture into a loaf pan or small baking dish and freeze the mixture until soft-frozen, about 4 hours.
While the semifreddo freezes, toss berries with the lemon juice and remaining 1/4 cup of sugar in a small bowl. Lightly mash with a fork to crush some of the berries. To serve, spoon the semifreddo into individual dessert dishes, top with some of the berry mixture and garnish with shaved chocolate.