For the salted caramel, melt sugar in a pan and caramelize until relatively dark. Deglaze with the coconut milk and boil down to a syrup. Season to taste with sea salt.
For the cake, cream butter with sugar and salt until very fluffy. Beat in eggs one at a time. Mix flour with baking soda and add to the mixture.
Peel bananas, cut into pieces and puree finely with milk using a hand blender. Mix the mashed bananas into the mixture.
Grease Rex glasses well with butter, fill the dough halfway and bake in the preheated oven at 160 °C for 25-30 minutes. Test with chopsticks.
Pour the salted caramel over the overcooled cakes and serve.