Mash the bananas well with the back of a fork. Use sweet, soft and fully ripened bananas with lots of black spots.
Put the butter and sugar in a pan and melt over medium heat. Stir the bottom occasionally to avoid scorching. About 3 minutes later.
It changes to brown caramel colour. Turn off the heat. Add the mashed bananas and mix quickly. Cook over low heat for about 3 minutes while stirring.
Add condensed milk and rum (if you like), and bring to a boil. Turn off the heat immediately once it comes to a boil. Don't overcook after adding the condensed milk.
This is the recipe photo from the book I referred to. It is made from sliced bananas, and I guarantee the taste! Try the original recipe as well.
Story Behind this Recipe
I referred to "Banana Stewed in Caramel Sauce" in the book "So 'Le Creuset', Good Food" written by Yukiko Hirano. I modified the recipe to make a cream or paste, so I mashed the bananas well, added more sweetness and tried to make creamier.
Keep in the refrigerator and finish within a week. Reheat the necessary amount of the chilled cream in a microwave before you eat if you like. The colour will not stay beautiful, but it will be taste nice.