In a saucepan of boiling salted water cook parsnips until tender; drain and puree through a food mill. You should have 2 cups of puree. Heat oil in a skillet and saute onion, pepper and celery 1 minute. Add garlic and corn, season to taste and toss well. Fold vegetables into parsnips. Pull back leaves of husk, fill with vegetable puree and tie shut with a piece of string.