Melt butter in a medium-sized sauté pan over medium heat, add plantains and cook until browned on one side. Flip and cook the other side until browned and remove from pan.
Add palm sugar to the butter and cook, stirring occasionally, until it turns a rich caramel colour. Once the sugar has darkened to the desired colour, immediately add coconut milk (it will bubble aggressively).
When the bubbling subsides, add salt and rum, if using. Stir over medium heat until the sugar is completely dissolved and the sauce has thickened slightly.
Add the plantains back in and cook just to heated through, about 30 seconds, flipping the pieces or baste the top with the sauce.
Remove from heat, serve over vanilla or coconut ice cream, and sprinkle with roasted chopped peanuts. Enjoy!