In a large bowl, mix together all of the ingredients until the sugar has dissolved.
Pour the mixture into the vessel of the Ninja Slushi machine.
Set to the Milkshake preset. Once the machine beeps, dispense and serve immediately.
Notes
Pulp-free juice is key. Always use pulp-free juice, as juice with pulp can clog the machine's freezing mechanism, and ruin the smooth texture.
Serve immediately. Because this recipe is made with dairy, leaving it in the machine for too long can over-churn the drink, causing it to have a more butter-like texture.
To prep ahead of time, mix all of the ingredients in a bowl and place in the fridge. When ready to drink, pour into the vessel of the Ninja Slushi machine and set to Milkshake. Do not try to freeze the drinks in drink pouches, as the dairy will break down when thawing.