1. Caramel: Melt the butter in a saucepan. Add the sugar and cream and cook over medium heat, stirring continuously until the sugar has dissolved.
2. Bring the sauce to the boil then simmer for 5 minutes. Remove from the heat and stir in the vanilla essence and salt. Set aside until cool.
3. Milkshake: Put the ice cream, milk and cinnamon in a measuring jug. Blend with a stick blender and add the Amarula (if using). Pulse until well combined.