Season the lamb with salt and pepper. In a large dutch oven, heat the olive oil over medium-high heat. Working in batches, add the lamb and cook, turning occasionally, until browned, about 10 minutes; transfer to a plate.
Add 1/2 cup white wine to the pot, scraping up any browned bits. Add the onion and garlic and cook until softened, about 5 minutes. Stir in the tomato paste, the remaining 1/2 cup white wine, the red wine, chicken broth and 3 sprigs thyme. Return the lamb and any juices to the pot and bring to a boil. Lower the heat to medium-low, cover and simmer until the lamb is tender and the sauce has thickened, 2 to 2 1/2 hours. Garnish with more thyme sprigs.
