Blueberry Tiramisu

Came across this recipe from the internet, from foodnetwork.com. I was attracted by the picture of the tiramisu but i noticed that it's actually a dessert, i would actually prefer something more like a cake so i made some changes here and there, made a sponge cake and sandwiched the tiramisu layer in between the cakes. Well, this is supposed to be called Lime and Blueberry Tiramisu but the flavour of the lime here is not significant at all, hence i just put this as blueberry tiramisu. The original recipe asked for lime concentrate.I dipped the sponge fingers in pure extracted lime juice but i must say that they have not been properly soaked..as for the tiramisu layer, to me it's good but i would prefer the mascarpone layer to be lighter and i was thinking if i have whisked some egg whites into mascarpone layer, would it turn out better? But the blueberries sure added points to this cake...something unusual from the classic tiramisu.

Ingredients and method for sponge cake ( for 9" square pan) can be found here

Ingredients for tiramisu layer
2 medium egg yolks
30gm sugar
250gm mascarpone cheese
80mls non diary whipping cream
50mls heavy cream

sponge fingers
blueberry pie filling

Method for preparing tiramisu layer
1. Whisk the egg yolks and sugar until pale
2.Add in the mascarpone cheese and just stir by hand to mix. Keep chilled .
3. Whisk the non diary whipping cream until slightly thick and add in the heavy cream and continue whisking
until soft med peaks.
4.Remove the mascarpone cheese mixture from the fridge and add the cream mixture(3) into the cheese mixture(2)

Method for assembling cake:
1. After sponge cake has cooled down, cut into 2 layers.
2. Dip the sponge fingers into lime concentrate or juice and arrange side by side on top of one layer of the sponge cake. Do this to fill up the whole cake.
3.Spread a layer of the blueberry pie filling on top of the sponge fingers layer and followed by the tiramisu layer
4.Cover with the 2nd piece of sponge layer and to finish the cake, top it up with another layer of blueberry filling. (Can also top this up just before serving.) trim the sides of the cake to look neat. Chill.