In a medium bowl, combine the sliced strawberries with the granulated sugar. Gently toss the strawberries until they are evenly coated. Let the mixture sit for 10-15 minutes at room temperature.
In a separate bowl, use an electric mixer to beat the heavy cream on medium speed until it begins to thicken. Gradually add the powdered sugar and vanilla extract, then continue whipping until soft peaks form.
If you are using sponge cake, slice it into evenly sized rounds. If you prefer ladyfingers, you can leave them whole.
In a 9x13 inch baking dish, start your layers by placing a single layer of sponge cake rounds or ladyfingers at the bottom.
Spoon a generous layer of the whipped cream mixture over the cake, spreading it evenly across the surface.
Next, add a layer of the macerated strawberries on top of the whipped cream, including some of the strawberry juice.
Continue to alternate the layers: cake, whipped cream, strawberries, repeating until the dish is nearly full. Finish with a layer of whipped cream on top.
Once assembled, cover the dish tightly with plastic wrap and refrigerate for at least 4 hours, or preferably overnight.
Just before serving, garnish the cake with fresh mint leaves and a few extra slices of strawberry.
Notes
For best results, refrigerate overnight to allow flavors to meld.