Place the potatoes into a medium pot and cover with cold water. Season the water with salt and place over medium-high heat. Bring up to a bubble, then reduce the heat to medium. Cook the potatoes until fork tender, 8-10 minutes. Drain the cooked potatoes and reserve in a colander.
Place the pot the potatoes were cooked in over medium-high heat with 1 turn of the pan of EVOO, about 1 tablespoon. Add the banana slices and cook until hot and very tender, 2-3 minutes. Add the potatoes back to the pot along with the stock or buttermilk and mash until they’re as smooth as you like them. Season with salt and pepper and serve.