Mashed Potatoes with parsnip

add to shopping list 1 tablespoon olive oil 3 large white onions, thinly sliced 2 tablespoons brown sugar 1/4 teaspoon salt 3 baking potatoes (such as Yukon[...]

2 tablespoons unsalted butter 4 ounces carrots (parsnips, turnips, or celery root, peeled, carrots or parsnips cut into 1/4-inch-thick half-moons, t) 3/4 lb[...]

4 russet potatoes , about 2 lb total, peeled and cut into rounds 1/4 inch thick 3 parsnips , about 3/4 lb total, peeled and cut into rounds 1/4 inch thick 4[...]