How to Make It
Preheat broiler. Place bell peppers on a small baking sheet, and roast under broiler or directly over a gas flame, turning frequently, until skins are blackened, about 5 minutes. Transfer to a medium heatproof bowl, and cover tightly with plastic wrap. Let stand until peppers are cool enough to handle, about 10 minutes. Remove and discard skins, stems, and seeds; place in a blender. Add tomatoes; process until smooth.
Season chicken to taste with salt and pepper. Melt butter in a large Dutch oven over medium-high. Add chicken thighs, and cook until browned, about 4 minutes per side. Transfer chicken to a plate.
Add bacon to Dutch oven, and cook, stirring, until bacon begins to render, about 2 minutes. Add onion and mushrooms, and cook, stirring occasionally, until onion begins to turn golden, about 5 minutes. Stir in fennel, leek, garlic, and paprika, and cook 2 minutes. Add kielbasa, dill, and parsley. Cook, stirring, until sausage is heated through, 3 to 4 minutes.
Return chicken to Dutch oven. Add wine, bring to a boil, and cook until liquid is reduced by half, about 5 minutes. Add pepper mixture, and bring to a simmer. Add stock and sauerkraut; stir to combine. Bring to a simmer, reduce heat, and simmer gently until vegetables are tender and chicken shreds when prodded with a fork, about 45 minutes. Season to taste with salt, and serve.