Place the bananas in a freezer-proof container and freeze for at least 3 hours.
Meanwhile, prepare your candied nuts as follows: If not roasted, toast the cashews in a heavy-based pan over medium heat until golden brown. Add the brown sugar, butter, maple syrup and cinnamon, and stir until well coated. Cook over medium-low heat, stirring, until the sugar has dissolved, a further 5 to 10 minutes. Remove the pot from the heat and pour its contents onto a nonstick baking sheet or silicone baking mat. Set aside to cool before breaking or chopping into rough pieces.
Once the banana pieces are frozen, place in a blender with the peanut butter, honey and milk; blitz until you have a smooth consistency. Serve immediately with a scattering of candied nuts, or return to the freezer for 15 to 20 minutes to firm up a little more if you prefer.