Peel 2 celery roots, trimming as needed to clean. Slice thinly across the root to make even slices and then cut these cross-wise to make julienne. (The safe way to do this is to cut the root lengthwise and then work with each half to make the thin slices.) Set the julienne aside. Despite what you might read elsewhere, they will not brown if you are going to cook with them for 3-4 hours.
When you are ready to cook them, heat some olive oil to coat the saute pan. Add the julienne and saute for about 10 minutes, or until they are soft and have some color. Season to taste with salt and pepper. Garnish with some chopped fresh parsley.