1 cup milk
1 1/2 cup Nutella (at room temperature)
2 cups cream
Heat cream until right before it comes to the boil (it will bubble along the edges). While this is heating, whisk together yolks, milk, 1 cup of Nutella and salt. Set aside.
Add a few cups of ice to a large bowl, set a smaller bowl in the large bowl, set a fine strainer on top and set aside.
When cream is heated, remove from heat and slowly whisk hot cream into the Nutella mixture. Pour mix back into the saucepan and stir continuously on medium heat until it thickens slightly. Turn off heat.
Pour custard through strainer into the small bowl. Add just enough water to the large bowl of ice so that the cold water rises up to level with the custard. Be really careful here you don't drop any water into the custard!
Stir occassionally until cool, then remove from ice bath and cover with plastic wrap. Refrigerate for several hours.
Mix ice cream in mixer on highest speed with whisk attachment.
Fill container with half of the ice cream. Drizzle 1/4 of a cup of Nutella over the surface. With a fork, swirl through the ice cream. Repeat with the rest of the ice cream and Nutella.
Freeze for a few hours or overnight.