Soup maker: I'm not a huge fan of soup makers I'm afraid. I had one a while back but found that the vegetables at the bottom of the jug tended to stick and burn whilst those at the top were barely cooked. Personal difficulties aside, although it's possible, this isn't the best soup to make in a soup maker. Although the tomato base needs to be blended, the rest of the vegetables do not. You'd have to empty out the vegetables once they have been allowed to sweat, then puree the soup base and add the vegetables back in before proceeding to the final cook. If you don't mind this extra step then feel free to use your soup maker. Slow cooker: similarly, a typical slow cooker isn't ideal for this fennel soup recipe either. Unless you have a slow cooker that allows the bowl to sit on the hob then you'll still need to sweat the vegetables in a pan before adding to the slow cooker and life is too short for dealing with extra washing up. You could, however, use a slow cooker to keep the soup warm at a party.