Slice the bananas into 2cm (¾in) chunks and place in a single layer on a baking tray. Freeze until solid. You can keep them in the freezer until you are ready to make the ice cream.
Put the frozen banana chunks into a food processor along with half of the nuts, half of the maple syrup and the salt, and process until smooth and creamy.
Chop the remaining nuts and add to the mixtu