First you need to make your custard base. In a large saucepan place the cream and milk in and very gently heat it up until it is steaming but not boiling. You don't want it to boil because this will scramble your eggs when it is added to them.
While the milk and cream are warming up, whisk the egg yolks in a heat proof bowl together then add the sugar and whisk until pale. A couple of minutes should do it. I highly recommend using an electric whisk or stand mixer, especially for the next step.
Once the cream and milk are all steamy, very slowly begin to pour it into the egg yolks whisking all the time. Keep pouring until all the cream milk mixture is incorporated.
Then return the mixture to the pan and gently heat again over a low heat not allowing it to boil. Keep stirring until the mixture coats the back of your spoon.
Split the mixture between two heat proof bowls its going to be approximately 550 millilitres (2 and 1/4 cups) in each bowl.
In one of the bowls add the white marshmallows and stir until they melt this won't take long.
Now leave the bowls at room temperature. Returning to them every 5 to 7 minutes to give them a stir to prevent a skin from forming. Once they are at room temperature cover them and place them in the fridge for at least 6 hours preferably overnight if you can.
Its now time to churn your ice cream. As recommended earlier I would make the marshmallow ice cream first its flavour is more delicate than the peanut butter one.
If your marshmallow custard has set a bit don't worry add the tablespoons of milk and give it a quick mix with a fork or hand whisk and it will liquify again. In accordance with your manufactures guidance make your first batch of ice cream.
In my KitchenAid ice cream bowl I have to attach the correct attachments turn them on then add the custard and churn for 20 to 25 minutes.
When the ice cream is made quickly scoop it out into a suitable tub, only using one side of the tub so you can later add the peanut butter ice cream next to it. Pop it in the freezer to stay solid.
Working quickly blend in the peanut butter with your other custard till smooth using an electric hand blender or liquidiser then turn on your ice cream maker again and pour in the new custard.
Again follow your manufactures instructions, mine took about 20 to 25 minutes.
Scoop the peanut butter ice cream in next to the marshmallow ice cream and with a spoon gently swirl the two together a little bit. Then swirl in the peanut butter and marshmallow fluff very gently to give a nice swirly pattern.
If using scatter a few peanut butter chips and mini marshmallows on top for decoration. Place a lid on your tub and pop it back in the freezer for at least 2 hours to harden.
This ice cream will keep in your freezer for up to 3 months - it has almost all gone in my house and its only been in the freezer for 5 days!!!