Roast the peppers by charring them over an open flame on a gas stovetop or under a broiler on high until skins evenly blacken and the flesh is tender. Place peppers in a bowl and cover; let cool so they can be handled. Peel, seed and stem the peppers then quarter the peppers lengthwise and slice into strips.
Place porcini mushrooms in a medium saucepot and cover with stock. Bring to a low boil and simmer to reconstitute and reduce the stock by a third.
Meanwhile, tie herbs in bundle with kitchen twine. Pat the chicken dry and season with salt and pepper.
Heat a large Dutch oven over medium-high heat and preheat oven to 325°F. Add oil, 2 turns of the pan, then add chicken in 2 batches and brown until crispy on both sides; remove to a plate. Add onions, celery, garlic and chili pepper, and season with salt and pepper. Stir to soften a few minutes then add tomato paste to the pot and stir a minute more; add wine and reduce by half.
Remove porcini from stock, chop and add to sauce. Add stock and canned tomatoes, breaking them up a bit. Add herb bundle and the browned chicken to the pot then cover, place in the oven and roast 60 minutes.
Remove chicken and some sauce to a serving platter or plates with extra sauce in another dish for passing. Serve crusty bread for mopping or toss some of the extra sauce with pappardelle and serve alongside chicken.