Even past its prime it would be tasty roasted a while with just some olive oil and seasonings
I’ve made celeriac soup but I don’t think I followed a proper recipe- i do recall i needed to add some potatoes to get a nice smooth texture.
Fennel celeriac soup is a popular combo, although would also need some potato to make smooth.
Or you could follow a recipe for your favorite chowder style soup/stew and swap in the celeriac for part of the potatoes
