If you have time, preheat the oven to 180°C. Add the tomatoes to a baking tray and roast for 25 minutes.
Add to the slow cooker with all the remaining ingredients, except the tortellini. Cook on high for 3 hours or low for 5 hours.
Blitz with a handheld blender, then stir in your tortellini and cook on high for 10–15 minutes. Serve in bowls, garnished with extra basil leaves.
