Preheat oven to 200°F and line a sheet pan with parchment paper.
In the bowl of an electric mixture, beat the egg whites on medium-high speed. When the egg whites form soft peaks, slowly add the sugar. Beat the egg whites on high until stiff peaks form. Gently fold in the powdered sugar.
Spoon the meringue onto the parchment paper and smooth the top(s) if necessary. Bake for approximately 2 hours, or until the the surface of the meringues appears hard and dry. Cool completely.
When ready to serve, whip the whipping cream, adding the sugar and flavoring during the last 30 seconds or so of whipping. Spoon over the baked meringue and top with berries.