Prepare the soursop by cutting it, or breaking it open, in half, lengthwise. Remove and discard the spine. Scoop the flesh with seeds into a small saucepan with the juice or water and warm the flesh over medium heat to draw out the juices. Push the flesh mixture through a sieve to extract the liquids. Discard the seeds and remaining flesh. Set aside.
Set up an ice water bath in a large bowl, or clean sink for later.
In a medium heatproof bowl, whisk together the egg yolks and sugar until fully incorporated and pale. Set aside.
In a medium saucepan, warm the milk, cream and vanilla bean and pod to a light boil. Remove from the heat and drizzle half into the egg mixture, while whisking. This tempers the egg/sugar mixture. Add to the remaining cream/milk mixture in the saucepan and return to a light boil, allowing it to thicken.
Add the soursop to the egg/cream mixture and continually stir the mixture with a wooden spoon until it thickens and coats the back of the spoon. Run your finger along the back of the spoon and it should leave a clear line through the mixture on the spoon.
Remove from the heat and quickly cool the mixture by placing the saucepan in the water bath, stirring the mixture to help the cooling process. Zest the lime into the mixture, cover and place in the refrigerator for 4 hours, or overnight for a more pronounced flavour.
Once chilled, remove the vanilla pod. Freeze the mixture in an ice cream maker according to the manufacturer's instructions. I use the KA ice cream attachment, which took about 20 minutes. Transfer to a freezer-safe containe and allow to chill overnight.