To a mixing bowl, add the custard and cream alternative, mix with a balloon whisk.
To another bowl, add the milk, sweetener and vanilla. Whisk with a balloon whisk until the sweetener has dissolved.
Pour the milk mixture into the custard mixture and mix until combined. Pour into your Ninja Creami tub. Pop the lid on and freeze for 24 hours.
Remove the tub from the freezer and use the light ice cream function on your Ninja Creami machine. If your ice cream looks chalky or not a nice creamy consistency, use the re-spin function. We used the light ice cream function once and re-spin twice.
Make a hole in your ice cream to the bottom of the tub about 2-4cm wide. Add your crushed biscuits and use the mix-in function on the machine. Serve.