In a medium size saucepan, dissolve 100g of sugar with 300ml of water on a medium heat. Cook for 5 minutes and stir occasionally.
Transfer 80ml of the sugar syrup into a bowl, pour in the Limoncello, mix well and set aside to cool.
Add the blueberries in the pan with the remaining sugar syrup and cook on a medium heat for 2 minutes until they are beginning to release some juice.
In a drinking glass, mix the arrowroot with 2 tablespoons of cold water and stir until smooth. Pour in the pan with the blueberries and cook for a further minute, keep stirring. Allow to cool. (Reserve some berries to decorate).
Place the egg yolk with the remaining sugar in a large bowl and whisk until pale and thick. Beat in the mascarpone and the lemon curd.
In a separate clean, dry bowl, beat the egg whites until soft peaks form. Gently fold into the mascarpone and lemon curd mixture.
Place a layer of Pandoro in a large 1.5litre glass serving dish. Brush with a third of the Limoncello syrup, then spread with a third of the curd mixture. Add in a third of the berries and their syrup.
Repeat the layers, then top with a final layer of cake. Brush with the remaining Limoncello syrup and top with the remaining curd mixture.
Cover with clingfilm and chill for 5 hours or overnight.
To serve, whip the cream to soft peaks and spread evenly over the trifle. Scatter with the reserved blueberries and toasted flaked almonds.