Preheat oven to 350. Grease 9 1/2 pie plate (use a glass deep-dish).
Clean chard well. Separate stems from leaves; cut off bottom 2 inches of stems. Slice stems thin and coarsly chop leaves.
Using a 12 inch skillet, heat oil. When hot, add stems and stirring frequently until browned (about 5 minutes). Add onions, salt and pepper; cook 1 minute. Add leaves and cook about 5 minutes, sitrring frequently until wilted and any water is gone.
Wisk together in a large bowl the eggs, milk, ricotta, parmesan cheese and cornstarch; then add chard mix.
Pour into prepared pie plate. Bake 40 minutes or until knife inserted 2 inches from center comes out clean.