First, make the strawberry puree. Wash the strawberries and cut the greens off. Set aside about 10 nice looking strawberries for the decorating. Puree the rest of the strawberries in a blender.
In a sauce pan, heat up about a third of the strawberry puree with 80 g of sugar and the powdered gelatine. Boil for 1-2 minutes (whisking continuously) until the sugar has dissolved. Remove from the heat and whisk in the rest of the strawberry puree. Set aside to cool.
Make the syrup for the ladyfingers. In a small saucepan, heat up the water with 80 g of sugar and the zest of the lemon. Stir until the sugar has dissolved. Set aside to cool.
Next you can make the strawberry mousse. In a large bowl, whip up the cream to a firm peak. Gently fold in the strawberry puree, using a spatula. Do not overmix, the mixture should be still airy.
Line a 20 cm round spring form cake pan with baking paper (both bottom and sides).
Soak the flat side of the ladyfinger in the syrup and place against the side of the cake pan (soaked side facing inside). Repeat and arrange most of the ladyfingers (about 18) around the sides of the cake tin. Soak the rest of the ladyfingers and place on the bottom of the cake pan in one layer (you can break them apart to make an even bottom for the cake).
Pour the strawberry mousse in and smooth the top with a spatula. Place the cake in the fridge to set overnight. (I prefer setting my cake overnight, but about 4-6 hours is probably enough if you want to serve it sooner!)
When the cake is set, remove the sides of the springform cake tin and peel off the baking paper from the edges. The cake should stay in its shape easily (if not, put back to the fridge to set more).
Mix the cream cheese and icing sugar until creamy. Put the mixture into a piping bag and pipe on top of the cake. Decorate with fresh strawberries.