Put the yolks and sugar into a large
bowl, then use an electric whisk to
beat together until pale and thick.
Meanwhile, put the milk, mascarpone,
vanilla and orange zest into a medium
saucepan and bring to the boil, whisking
to blend the mascarpone into the milk.
Once just boiling, take off the heat and
whisk this gradually into the egg mix to
make a custard.
Clean out the pan, then tip the custard
into it. Cook gently for 15 mins, stirring all
the time, until the mix is thick enough to
coat the back of a wooden spoon. Don’t
let it boil or the eggs will scramble. Sieve
into a bowl and leave to cool.
Churn in an ice-cream machine until
thick and smooth, then tip into a plastic
container. Spoon over the marmalade,
then use a skewer to ripple the
marmalade through. Cover and freeze
for at least 6 hrs until set. If you don’t
have an ice-cream machine, freeze the
custard for 4 hrs in a container, stirring
and breaking up the crystals every hour
until thick and smooth. Swirl in the
marmalade, then freeze solid.