Peel the potatoes, cut them into coarse pieces and put them in a suitable container along with the finely chopped celery.
Pour on water, enough to submerge the vegetables and bring to a boil. Boil on low heat until the potatoes soften, then add the crumbled feta and blend.
Season the puree with salt and black pepper to taste, add the butter and stir well.
Serve it while still warm as a garnish to roasted meat.