1
Adjust rack to top and bottom positions and preheat oven to 425 degrees. Wash and dry all produce. Cut potatoes into ½-inch-thick wedges. Halve, peel, and very thinly slice onion. Pick 1 tsp thyme leaves (2 tsp for 4 servings) from stems; reserve remaining sprigs for step 2. Cut tomato into 8 wedges (16 for 4). Halve lemon.