Add the avocado flesh to a blender. Pour in the key lime juice, followed by the sweetened condensed milk, 2 graham crackers, and finally the whole milk. Blend until completely smooth. Adding the ingredients in this order helps prevent the milk from curdling from the acidity of the lime juice.

Pour the mixture into a Ninja Creami pint container. Freeze on a level surface for at least 24 hours.

Remove the pint from the freezer and process using the Ice Cream cycle.

Add 1 tablespoon of whole milk and run the Re-Spin cycle.

Crumble the remaining graham cracker over the top or use it as a mix-in before serving.