Fill a small bowl with 60g of cold water. Sprinkle gelatin powder over the water. Let this sit for at least 10 minutes to bloom the gelatin (it will become a firm gel puck).
Line the sides of a 9" springform pan with parchment paper or clear acetate.
Cut about ¼" off one end of the ladyfingers that will be going around the side of the pan (about 23 ladyfingers) so that they can stand up vertically. Arrange them in a ring around the pan.
Arrange a layer of ladyfingers on the bottom of the pan, cutting them smaller where needed to fill in any gaps. Add an even layer of about 200g of the diced strawberries on top of the ladyfingers. Set aside.
In a large mixing bowl, add the whipping cream, powdered sugar, and vanilla extract. Use an electric hand mixer fitted with a whisk attachment to beat the cream until it becomes firm peaks. Separate out about 100g of whipped cream into a piping bag fitted with a piping tip of your choice for the topping. Set both aside.
To a blender, add 250g of the diced strawberries. Microwave your small bowl of bloomed gelatin for about 15 seconds until it has melted into a liquid. Add this to the blender. Blend until the strawberries have been pureed.
Pour the pureed strawberry mixture into the bowl of whipped cream. Fold them together with a spatula until no streaks remain.
Add about half of this strawberry mousse mixture into the pan on top of the strawberry layer. Smooth into a flat layer with a spatula.
Arrange another layer of ladyfingers on top. Add the rest of the diced strawberries on top. Finally, add the rest of the mousse mixture on top and smooth the top with a spatula.
Pipe a ring of whipped cream on top of the cake. Arrange strawberries on top as decoration.
Chill the cake in the fridge for at least 6 hours or preferably overnight for the mousse to firm up and the ladyfingers to soften. Release the cake from the pan and tie a ribbon around the cake before serving.