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1
Preheat the oven to 350 degrees F (175 degrees C). Place a rack in the middle of the oven.
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2
Heat a 6 1/2 quart Dutch oven on the stove over high heat. Sear chicken thighs, skin-side first, in the hot Dutch oven, flipping over halfway, until browned, 6 minutes. Season with Italian seasoning, salt, and black pepper. Transfer chicken to a plate, skin-side down. Drizzle vinegar on top.
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3
Add sausage and mushrooms to the Dutch oven over medium-high heat. Cook until sausage is browned, 3 to 5 minutes, adding a little vinegar if the pan is too dry. Drain and discard grease. Pour spaghetti sauce into the Dutch oven and stir. Return chicken to the Dutch oven, skin-side up, leaving skin exposed above the sauce. Cook until sauce begins to bubble, 3 to 5 minutes.
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4
Transfer Dutch oven to the preheated oven and bake 30 minutes.
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5
Meanwhile, bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water, stirring occasionally, until partially cooked, about 4 minutes. Drain and rinse with cold water to stop the cooking process.
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6
Remove Dutch oven from oven and add cooked spaghetti noodles on top. Use tongs to pull chicken thighs above the noodles and to push noodles down into sauce. Top everything with shredded Italian cheese blend and return Dutch oven to the oven for 10 minutes more. Turn on the broiler and broil 5 minutes.
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7
Remove Dutch oven and let cool about 10 minutes before serving.
