Make sure the freezer's ice cream base is in the freezer for at least 24 hours so it is ready.

Preheat the oven to 350°F. Spread the pistachios on a baking sheet and toast in the oven for 4-5 minutes until fragrant, turning once. Don’t over-toast or the pistachios will lose their green hue. (alternately, toast in a frying pan on the stovetop)

Remove from oven. Set aside 1/4 cup of pistachios for later. Put the remaining 1/2 cup toasted pistachios into a food processor and pulverize until pistachios form a coarse paste. Add a few drops of water if necessary.

Transfer pistachio paste to medium bowl and mix with cream cheese and salt until smooth.

In tiny bowl, mix cornstarch with 2 Tablespoons milk until smooth. Set aside.

Prepare a large bowl of ice cubes and water to use later for cooling the ice cream.

In a medium saucepan, combine remaining 2 cups and 2 Tablespoons milk with the cream, sugar and corn syrup. Bring to a rolling boil over medium to medium-high heat.

Boil for 4 minutes. (Note that milk will quickly foam up high if it’s too hot, so use a high-sided pan than can handle this and do not leave the stove unattended. Be ready to lift the pot off the heat quickly and have a place to put it down!)

Reduce heat to low. Slowly mix in the cornstarch/milk mixture.

Bring back to boil and cook, stirring constantly until slightly thickened, 3 to 5 minutes. Remove from heat.

Gradually whisk the hot milk mixture into the pistachio paste. Whisk until well blended.

Pour into a clean glass pitcher or large Ziploc bag and submerge (seal Ziplock first) into the ice bath. Let stand, adding more ice if necessary, until cold, about 30 minutes.

Transfer ice cream liquid to refrigerator and chill completely, for about 6 hours or overnight.

Coarsely chop the remaining 1/4 cup toasted pistachios.

Prepare a storage container with airtight lid, which can be pre-chilled in the freezer.

Turn on the ice cream machine and gradually pour the ice cream mix into the base through the top of the machine. Add the rosewater to the machine after it has been churning for 15 minutes. Leave to spin until thick and creamy, about 18-25 minutes total.

Working quickly, pack half the ice cream into the prepared storage container. Sprinkle the remaining chopped pistachios over it in a layer (**see note), then sprinkle the marshmallow bits over the nuts (if using). Spread the remainder of the ice cream over the top of the fillings.

Seal and put the container in the freezer for at least 4 hours so it can freeze completely.

Garnish with more pistachios, if desired.