The simplicity of the meringue is enriched by the combination of the berries and Chambord liqueur.
Make meringues: Preheat oven to 180 degrees. Add egg whites to the bowl of an electric mixer fitted with the whisk attachment; beat on medium-low speed until soft peaks form, about 5 minutes. With mixer running, slowly pour in granulated sugar; beat on high speed until stiff, glossy peaks form, about 5 minutes.
Remove bowl from mixer; sift confectioners' sugar over top of meringue; fold in gently. Spoon 1/2-cup mounds of meringue onto parchment-paper-lined baking sheets. Make an indentation in the center of each with the back of a spoon; swirl sides. Bake until dry and firm and release from parchment paper when pulled, about 1 1/2 hours. Let cool completely.
Make sauce: Cook strawberries and sugar in a small saucepan over medium heat, stirring constantly, until strawberries start to release juices, about 1 minute. Stir in blackberries; cook until saucy, about 8 minutes more.
Meanwhile, combine Chambord with cornstarch in a small bowl. Bring fruit mixture to a boil; stir in cornstarch mixture. Boil gently 1 minute, then remove from heat. Let cool completely. Divide sauce among meringue just before serving.