In a medium bowl, prepare the vanilla pudding by whisking together the pudding mix, milk, and vanilla extract until smooth. Refrigerate for about 5 minutes to thicken.
In a large trifle dish or individual serving glasses, layer half of the cubed pound cake at the bottom.
Spoon half of the prepared vanilla pudding over the pound cake layer.
Add a layer of half of the sliced strawberries and half of the blueberries on top of the pudding.
Spread half of the whipped cream over the fruit layer.
Repeat the layers with the remaining pound cake, pudding, strawberries, blueberries, and whipped cream.
Finish with a dollop of whipped cream on top and garnish with fresh mint leaves if desired.
Chill the trifle in the refrigerator for at least 1 hour before serving to allow the flavors to meld.