Prepare the Vegetables: Slice the onion and cut the carrots into rounds. Peel and rinse the small potatoes. Chop the garlic cloves roughly.
Season and Brown the Chicken: Season the chicken thighs with salt and pepper. In a preheated casserole on medium heat, brown the chicken thighs skin side down first, then on the other side until they start to become crispy.
Cook the Vegetables: Remove the chicken thighs and in the same fat, brown the onion and carrots for 3-4 minutes. Add the butter and garlic, cooking until fragrant.
Make the Sauce: Sprinkle with flour, then add white wine or water mixed with vinegar, stirring until partly absorbed. Add chicken stock, scraping the bottom of the casserole.
Add Tomatoes if Desired: For a tomato version, add the tomato pulp or crushed tomatoes.
Bake the Dish: Return the chicken to the casserole, add the potatoes, thyme, and chili pepper. Season with salt, cover, and bake at 180°C (356°F) for about 50 minutes.
Final Touches: After baking, add a sprig of rosemary, cover, and let stand for 15 minutes. Serve with fresh herbs like parsley or chives.