Combine milk, 1 cup of heavy whipping cream, sugar, and salt in a medium saucepan over medium heat. You want to heat the milk mixture up until hot, but not boiling.
Meanwhile, whisk the egg yolks in a small bowl and set aside.
Pour the remaining 1 cup of heavy whipping cream into a medium size bowl and top it with a fine mesh strainer. Set aside.
When the milk mixture is hot, slowly ladle an amount into the egg yolks, whisking continuously to temper the eggs. Pour the tempered eggs into the saucepan with the rest of the milk mixture, and whisk constantly over medium heat. The mixture will be ready when it has thickened and coats the back of a spoon, or the temperature reaches 170°F.
Immediately strain the custard into the prepared cold heavy cream and stir to stop the custard from cooking. Place the bowl of custard over an ice bath and allow the custard to cool completely, about 30 minutes. Cover and refrigerate until ready to churn, 4 hours or overnight.
To make the raspberry sauce, combine raspberries, sugar, and cornstarch in a small saucepan over medium heat. Stir in water. As the raspberries heat, they will release their juices, and the sauce will thicken. Remove from heat and use a potato masher or a fork to mash up the berries. Pour the sauce through a fine mesh sieve into a small bowl. You will have a smooth seedless sauce. Cover and place the sauce in the refrigerator until cold.
When you are ready to churn the ice cream, stir in vanilla extract and peach puree to the cooled custard base. Transfer the ice cream to an ice cream maker and churn according to the manufacture's instructions.
Transfer the ice cream into a freezer safe container. Dot raspberry sauce over top of the ice cream, and using a spoon, gently swirl the sauce throughout. Do not over mix. You want obvious swirls through the ice cream.
Cover and freeze the ice cream until it is ice cream consistency, about 8 hours.