Celeriac and butter bean soup with truffle-popcorn croutons

It may not be the prettiest of vegetables, but when peeled and cooked, celeriac has the most amazing flavour. Similar to celery, but with a sweet, nutty taste, it goes really nicely with the mellow creaminess of butter beans. If you want to create a real talking point, you can spruce up your soup by scattering some truffle and cheese-flavoured popcorn over the top. The popcorn is really easy to make and tastes unbelievably good.