Place a 1lb loaf tin in the freezer to chill before hand.
In a large glass mixing bowl, whisk the egg yolks and allulose.
Place the bowl over a saucepan of simmering water on a medium heat and whisk for at least 8 minutes until the mixture is light, thick and doubled up in volume.
Remove the egg mixture from the heat and cool.
Mix in the mascarpone, lemon juice and zest and stir until combined.
In another medium bowl, whisk the cream until it is stiff.
Fold the cream into the mascarpone mixture.
Pour the mixture into the loaf tin and spoon the hibiscus jam on top. With a spoon or knife, swirl the jam into the mixture.
Freeze for at least 4 hours before serving.
Store any leftover ice cream in an airtight container.