For the caramel macadamia mixture, place the sugar, cream and butter in a small saucepan and bring to the boil, stirring occasionally. Add macadamias and stir to combine. Remove from heat and set aside until ready to pour over the cake.
For the cakes, preheat oven to 180°C. Grease a 12-mould capacity muffin tin and line only the base of each muffin space with baking paper. Cream the butter and sugar. Add the eggs, one at a time, beating well after each addition. Stir in the bananas, followed by half the sifted flour. Combine the sour cream and milk, and then mix in half of it. Repeat with remaining flour and sour cream mixture.
Pour into the prepared tin so the mixture comes half way up the sides of each muffin space and place on the middle rack of the oven for 20-25 minutes, until the cakes are just set in the centre. Remove from the oven.
Use a large spoon to spoon over the caramel macadamia mixture so that each cake has 4 or so macadamias on top and continue to bake for a further 10 minutes until the caramel is bubbling and the macadamias golden.
Allow the cakes to cool in the tin for at least 15 minutes before gently removing by running a knife around the edge and lifting out.
Serve individual cakes with a scoop of ice cream.