01 -
In a small saucepan, whisk together 1/4 cup sugar, cornstarch, and 1/4 teaspoon kosher salt. Add cherries and raspberries, then bring to a boil over medium-high heat, stirring frequently. Boil for 1 minute, then stir in lemon juice and elderflower liqueur.
02 -
Transfer the cooked fruit mixture to a food processor and blend until smooth. Pass the purée through a medium-coarse-mesh sieve, discarding solids. Reserve approximately 1 1/4 cups (310 ml) of purée.
03 -
In a large heatproof bowl set over simmering water, combine whole egg, egg yolks, remaining 1/2 cup sugar, and 1/4 teaspoon kosher salt. Whisk until warm (about 160°F/71°C) and sugar dissolves.
04 -
Using an electric mixer, beat the warm egg mixture on medium-high speed until thickened and cooled, approximately 3 to 5 minutes.
05 -
Reduce mixer speed to low and gradually beat in 1 cup (240 ml) of the reserved berry purée until fully combined.
06 -
In a separate bowl, whip 3/4 cup (180 ml) heavy cream to stiff peaks. Gently fold whipped cream into the berry-egg mixture until homogenous, yielding about 3 1/2 cups (825 ml).
07 -
Divide mixture evenly among 8 freezer-safe glasses. Cover with plastic wrap and freeze until firm, at least 8 hours or up to 3 days.
08 -
Remove semifreddo from freezer 10 minutes before serving. Whip remaining 1/2 cup (120 ml) heavy cream to soft peaks. Spoon reserved berry purée over semifreddo, then garnish with fresh raspberries, cherries, and whipped cream.