Preheat oven to 375 degrees. Heat olive oil in an oven proof Dutch oven, add sausages and cook until evenly browned, remove and set aside. To Dutch oven add onion, garlic, carrot and celery and saute for 5 minutes. Add remaining ingredients, sausages and 2 cups of water to Dutch oven. Bring to a boil and put on middle rack in preheated oven and bake for 45-60 minutes, until thickened. Ladle generous portions onto toasted sourdough slices. To finish give a quick drizzle of olive oil and a few small leaves of fresh thyme.