Preheat the oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper.
In a bowl, sift together the flour and half of the sugar. Set aside.
In a separate large bowl, beat the egg whites with the cream of tartar until soft peaks form. Gradually add the remaining sugar and continue beating until stiff peaks form.
Gently fold the flour mixture into the egg whites until just combined. Stir in the vanilla extract.
Pour the batter into the prepared pan and bake for 30-35 minutes, or until the cake is golden and springs back when touched.
Let the cake cool completely. Top with mixed fresh berries before serving.
Notes
For best flavor, use berries that are in season and serve chilled.