Altered ingredient amounts.
I used Marie biscuits as that's all I had on hand, I also used raw sugar, just popped it in the blender with the biscuits for the crust, then used the blender again for the remaining sugar in the recipe. I might have measured my butter a bit short, the crust was too crumbly. If/when I make it again, I'll come and edit this tweak, once I'm sure if I did measure right or not!!
Seriously thinking of adding some cocoa powder to the mix next time, and replacing the lemon with vanilla (maybe as per the other tweak), as the children found it a bit tangy.