Pat the chicken thighs completely dry with paper towels. Season generously on all sides with salt and pepper. Place the flour in a shallow dish and lightly dredge each chicken thigh, shaking off the excess.

In a large Dutch oven or heavy-bottomed pot, heat the olive oil and butter over medium-high heat. Working in batches to avoid overcrowding, place the chicken thighs skin-side down and sear for 3-4 minutes per side, until deeply golden brown. Transfer the seared chicken to a plate and set aside.

Reduce the heat to medium. Add the chopped onion, carrots, and celery (mirepoix) to the pot. Sauté for 6-8 minutes, stirring occasionally, until the vegetables have softened.

Add the minced garlic and cook for another minute until fragrant. Pour in the white wine to deglaze, using a wooden spoon to scrape up any browned bits from the bottom of the pot. Allow the wine to simmer and reduce by about half, about 3-4 minutes.

Stir in the crushed tomatoes, chicken broth, bay leaves, and fresh thyme sprigs. Bring the sauce to a gentle simmer and season with salt and pepper to taste.

Return the seared chicken thighs to the pot, nestling them into the sauce. Ensure the skin-side is facing up. Reduce the heat to low, cover the pot, and let it simmer gently for 45-60 minutes. The chicken should be cooked through and tender enough to easily pull from the bone.

Remove the bay leaves and thyme stems from the sauce. Serve the Chicken Thigh Osso Bucco hot, spooning plenty of the rich sauce over the top. Garnish with fresh parsley. It's delicious served with creamy risotto, polenta, or mashed potatoes.