French Onion Soup with Roasted Poblano

Melt butter in a large Dutch oven over medium until sizzling. Add onions, bay leaves, thyme sprigs, salt, and pepper; stir to coat onions in butter mixture. Cover and cook, stirring occasionally, until onions are translucent and have cooked down to about half of their original volume, 20 to 25 minutes. Uncover and cook, stirring occasionally, until most of the liquid has evaporated and onions begin to stick to bottom of Dutch oven, 35 to 40 minutes. Cook, stirring often with a wooden spoon to scrape up any browned bits and adding splashes of water to deglaze the bottom of the pan, until onions are jammy and deeply browned, about 40 minutes.

While onions cook, roast poblano chiles, 1 at a time, over a medium gas flame, turning with tongs occasionally, until blackened all over, 10 to 12 minutes. Place charred chiles in a small bowl, and cover with plastic wrap. Let steam 10 minutes. Rub charred skin off chiles; discard skin. Cut chiles in half; remove and discard seeds. Slice chile halves into thin strips; set aside.