Remove corn from husk, leaving husk intact and discard corn silk. Cut kernels from cob and reserve; reserve cobs for next recipe. 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. Arrange a rack in a shallow pan or use a bamboo steamer. Place tamales in steamer and add enough water to steam, but not enough to get tamales wet. Cover tightly with a lid or with foil and steam 40 minutes. Serve drizzled with chili sauce.