In a medium mixing bowl, combine the sugar and milk. Using caster sugar helps it dissolve quickly, but regular white sugar may take a bit longer.
Add the cream and vanilla, then whisk until well combined.
Pour the mixture into the 470ml Ninja Creami tub, filling it just below the max fill line.
Freeze the mixture for 16-24 hours with the lid off.
Once frozen, process the ice cream using the ice cream function. The texture should be perfect after the first spin.
Create a small hole in the center of the ice cream and crumble 2 cookies into it. Replace the lid and use the mix-in function. If the cookies stay at the top, either stir them in manually or try respinning the ice cream. Note that multiple respins may soften the ice cream, requiring additional chilling.
For serving, optionally crumble 2 more cookies on top for extra texture.
Store any leftovers in the freezer with the lid on. Ice creams with a creamy base typically don't need to be respun when you want to enjoy them later.