Pour the milk and heavy cream into a medium-sized saucepan; set it over medium-low heat. Once hot, add the rose petals, marshmallows and mangos, cooking for about 10-15 minutes until the marshmallows have dissolved, stirring occasionally, but don’t let mixture come to a boil. Remove the saucepan from the heat.
In a large mixing bowl, whisk the egg yolks until they become thick and spongy.
Slowly stir 1/3 of the milk/cream mixture into the egg yolk, whisking, until thoroughly combined. Pour the egg mixture back into the saucepan with the remaining milk/cream mixture.
Set the saucepan over low to low-medium heat, stirring frequently with a whisk or spoon until the mixture thickens, about 15 minutes. Remove the saucepan from the heat. Once it cools, refrigerate.
Once chilled, process in an ice cream maker following the manufacturer’s instructions, and add the toasted pistachios 5 to 10 minutes before the ice cream is ready. Alternatively, freeze the entire mix.