Place all remaining ingredients in a slow cooker and season with salt and pepper. Stir well.
1 onion, 3 garlic cloves, 1 carrot, ½ cup beef stock, 1 celery stalk, 1 tbsp. olive oil, 6 oz. can tomato paste, 28 oz. can diced tomatoes, 1 cup pureed tomatoes, 1 tbsp. fresh basil, 1 tsp. fresh thyme leaves, Salt and pepper to taste