Peel and chop the potatoes and cook them in a pot of salted boiling water until fork-tender (about 12–15 minutes). Drain the water and mash the potatoes with a potato masher/ricer. Add a splash of plant-based milk for a creamier mash, then set aside.
Heat oil in a pan/skillet over medium-high heat and add the chopped onion. Sauté for 3 minut