Season the 2 1/2 pounds chicken pieces generously with kosher salt and freshly ground pepper on all sides. Heat the 2 tablespoons olive oil over medium-high heat in a large 5-quart braiser or Dutch oven. Once shimmering, add the chicken skin side down and cook undisturbed until golden brown, about 8 minutes. Flip and brown the other side. Transfer the chicken to a baking sheet.
Add the 1 pound spicy Italian sausage to the same pan and brown on both sides. Transfer to the baking sheet with the chicken.
Add the 1 medium diced yellow onion to the pan and season with salt and pepper. Cook, stirring occasionally, until it begins to soften and brown. Add the 2 cloves minced garlic and cook for about 30 seconds.
Pour in the 1 cup white wine and scrape up any browned bits from the bottom of the pan. Bring to a boil, then reduce to a simmer. Add the 28-ounce can crushed tomatoes and 1 3/4 cups chicken stock and stir to combine.
Return the chicken and sausage to the pan. Cover and gently simmer over low heat until the chicken and sausage are cooked through and the chicken is tender, about 40 minutes. Taste the sauce and add more salt if needed.
Meanwhile, bring a large pot of heavily salted water to a boil. Add the 1 pound small pasta and cook according to the package instructions. Drain and return the pasta to the pot. Spoon several spoonfuls of sauce over the pasta and toss to coat.
Transfer the pasta to a serving dish. Top with the chicken and sausage, spoon additional sauce over everything, and sprinkle with the 1/4 cup torn basil leaves before serving.