Heat a large Dutch oven over medium-high heat. Add EVOO, 2 turns of the pan. Add coarsely chopped carrots, celery, onion and garlic. Tie thyme and rosemary together with kitchen twine and drop into pot along with bay leaves. Season with salt and toss peppercorns into pot. Cover and cook veggies 6-8 minutes, stirring occasionally until tender-crisp. Turn off heat and let cool.
While the vegetables cool, bring a few quarts of water to a boil, add pearl onions and boil 3 minutes. Drain and cool onions in an ice water bath. Trim at root end and squish the onions away from their skins. Place in baggie and throw in fridge.