Pub-Style Shepherd’s Pie with White Cheddar & Thyme Mashed Potatoes

Heat broiler to high. Wash and dry produce.

Dice potatoes into ½-inch pieces. Strip thyme leaves from stems; roughly chop leaves. Trim, peel, and halve carrot lengthwise; slice crosswise into ¼-inch-thick half-moons. Finely dice celery. Halve, peel, and finely chop onion.