Season and sear the chicken. Pat the chicken dry and season with salt and pepper. Heat olive oil in a large Dutch oven over medium-high. Sear thighs skin-side down until golden and crisp, about 6–8 minutes.
Flip and cook 3 minutes more. Transfer to a plate.
Crisp the bacon. Add diced bacon to the pot and cook until lightly browned, 4–5 minutes. Spoon off excess fat if needed, leaving about 2 tablespoons in the pot for flavor.
Build the aromatic base. Add onion, carrots, and celery.
Cook, stirring, until softened and lightly golden, 6–8 minutes. Stir in garlic, tomato paste, paprika, thyme, and bay leaf. Cook 1–2 minutes until fragrant.
Deglaze. Pour in white wine, scraping up any browned bits.
Simmer 2–3 minutes to reduce slightly. Add tomatoes with their juices, beans, and chicken broth. Stir in Dijon mustard.
Taste and season with salt and pepper.
Nestle in the chicken. Return chicken thighs to the pot, skin-side up. The liquid should come about halfway up the chicken; add a splash more broth if needed.
Simmer and bake. Bring to a gentle simmer. Cover and transfer to a 350°F (175°C) oven.
Bake 35 minutes, then uncover and bake 15 minutes more to reduce slightly.
Make the topping. Toss breadcrumbs with olive oil, parsley, and a pinch of salt until evenly coated.
Add the crust. Sprinkle the breadcrumb mixture evenly over the cassoulet. Return to the oven, uncovered, for 10–15 minutes, until the top is golden and crisp.
Finish with acidity. Remove the bay leaf. Stir the vinegar into the beans around the chicken to brighten the flavors.
Let rest 5 minutes before serving.
Serve. Spoon into bowls, making sure everyone gets some crispy topping, creamy beans, and a piece of chicken. A simple green salad or sautéed greens pairs well.