Except for the celeriac and the black pepper, we can make the soup in the usual way, i.e. simmering the split pea with onion, leeks, carrots, potato, thyme, bay leaves and salt. Cook the celeriac separately. When the soup is done, take two portions, to make one portion without celeriac and the other portion without black pepper. For everybody else add the cooked celeriac and season it with pepper to taste. For one of the guest, you could replace the missing celeriac with mushroom for example and for the other replace the black pepper with a herb or another spice. If none of the three approaches can help alleviate your worry, you can still ask someone else to prepare or buy the special meal, or you can even explain and request the person concerned to provide her or his own food. Acknowledging our limitations can reduce pressure and anxiety.
The Jewel in the Cabbage 57