In a medium saucepan, combine heavy whipping cream, milk & sugar, place over medium heat
Cook until simmering
While getting the mixture up to temperature, take egg yolks in a separate bowl and whisk until a little lighter in color
Once cream mixture is warmed, take a ¼ measuring cup and slowly pour the cream mixture into the egg yolk whole while constantly whisking. Repeat 5 times
Once the egg yolks are tempered, slowly pour egg mixture into sauce pan while constantly whisking
Add vanilla and salt
Simmer until thickened, stirring constantly
Pour mixture into a bowl with a lid and place in fridge for 8 hours to cool, or longer. This can sit in your fridge for 2 days
Once cooled, churn in an ice cream machine until frozen
When the custard is fully churned, place the peanut butter in a microwave-safe bowl. Cook in the microwave for 30 seconds and stir.
Take a freezer safe ice cream container and scoop 5 larges spoonfuls of frozen custard into it. Pour 1/3 of the melted peanut butter on top. Repeat 3 teams until all the custard and peanut butter is used.
Stir a couple of times, folding the peanut butter into the ice cream and creating swirls.
Cover with a lid and place in the freezer for 4 hours to freeze solid and set.