In a large mixing bowl, combine the sliced strawberries, blueberries, and raspberries. Gently toss the berries together to mix them evenly.
In a separate bowl, whip the cream until soft peaks form. If using store-bought whipped cream, skip to the next step.
Add the powdered sugar and vanilla extract to the whipped cream, then continue to whip until stiff peaks form.
In serving glasses or bowls, layer the mixed berries and whipped cream. Start with a layer of berries, followed by a layer of whipped cream, and repeat until the glasses are filled.
Garnish with fresh mint leaves if desired. Serve immediately or chill in the refrigerator for up to 30 minutes before serving.