Mashed Root Vegetables

This dish is as easy to make as mashed potatoes and has a very pleasant, mellow flavor.  Clean and shave two fennel bulbs and peel two shallots and a celery root.  Chop the fennel into quarters and the shallots in half and the celery root into 2" chunks.  Steam the fennel and shallots until tender, then blend in a food processor until combined.  Set aside.  Steam the celery root until tender.  Place in a stand mixer and mash with the flat beater.  Add the fennel, shallots and a tablespoon of butter.  Mash until combined then switch the beater for the wire whip.  Whip on high until fluffy.  Keep in a warm oven until ready to serve as an accompaniment to roasted meat or poultry.