Ingredients
3/4 cup sugar
4 teaspoons cornstarch
1/2 teaspoon kosher salt
5 ounces sweet or sour cherries (fresh and pitted or frozen and thawed), plus more for serving
5 ounces fresh or thawed frozen raspberries, plus more for serving
1 tablespoon fresh lemon juice
3 tablespoons elderflower liqueur, such as St-Germain
1 large egg plus 2 large yolks
1 1/4 cups heavy cream
Preparation
Whisk together 1/4 cup sugar, cornstarch, and 1/4 teaspoon salt in a small saucepan. Add fruits; bring to a boil over medium-high heat, stirring frequently. Boil 1 minute, then stir in lemon juice and liqueur.
Transfer mixture to a food processor and purée, then pass through a medium-coarse-mesh sieve, discarding solids. (You should have about 1 1/4 cups.)
Combine whole egg, yolks, and remaining 1/2 cup sugar and 1/4 teaspoon salt in a large heatproof bowl set over (but not in) a pot of simmering water. Whisk until mixture is warm (about 160°F) and sugar has dissolved. Using a mixer, beat on medium-high speed until thick and cool, 3 to 5 minutes.
Reduce speed to low; beat in 1 cup berry purée. In a clean bowl, whip 3/4 cup cream to stiff peaks, then fold into berry mixture. (You should have 3 1/2 cups.) Divide mixture between 8 freezer-safe glasses and freeze until firm, at least 8 hours or, covered in plastic wrap, up to 3 days. (Meanwhile, refrigerate remaining berry mixture in an airtight container.)
To serve, remove semifreddo from freezer and let sit 10 minutes. Whip remaining 1/2 cup cream to soft peaks. Divide remaining berry mixture between glasses. Top with more raspberries, cherries, and whipped cream before serving.
