Heat the oven to 450ºF convection. (If you don’t have convection, don’t worry — your peppers may just take a little bit longer.) Place peppers in a 9×13-inch pan or baking dish. A sheet pan is not recommended because the balsamic can reduce too quickly and burn.. Coat the peppers with the olive  oil, and balsamic vinegar. Season with the salt and toss to coat.

Transfer the pan to the oven and cook for 15 to 25  minutes. Start checking at the 15 minute mark — every oven is different, and depending on the pan you are using the peppers may need more or less time. Remove the peppers when they look blistered to your liking — they shouldn’t be charred the way peppers look when you want to roast and peel them, but they should have some nice dark spots, and they should look wrinkly and slightly collapsed — they’ll collapse more once you remove them from the oven.

Remove the peppers from the oven and transfer them along with all of their juices to a serving platter. Taste for seasoning; sprinkle with more salt if desired. Garnish with optional thyme sprigs. Serve immediately or at room temperature.