Creamy White Bean and Vegetable Mash

extra-virgin olive oil, plus more for drizzling

onion, chopped

stalk celery, thinly sliced

carrot, peeled and thinly sliced

Yukon Gold potatoes, peeled and cut into 1-inch chunks

cooked white beans, drained (equivalent to one 16-ounce can)

Coarse salt and freshly ground pepper