Heat 120g sugar, orange zest, juice, and liqueur in a pan until sugar dissolves.
Dip half the sponge fingers into the warm syrup and line the bottom of a square dish.
Whisk egg yolks and remaining sugar over a pan of simmering water until the sugar melts.
Remove from heat and whisk yolks until pale and creamy, then transfer to a cool bowl.
Whisk egg whites in a separate bowl until stiff peaks form.
Beat the double cream until thick and fold in the mascarpone cheese.
Fold the egg yolks followed by the egg whites and vanilla extract into the cream mixture.
Layer the cream mixture and strawberries over the soaked sponge fingers.
Repeat the layering process and finish with a layer of strawberries.
Cover the dish and chill in the fridge for two hours.
Dust the top with icing sugar before serving.