Position rack in center of oven and preheat to 350°F. Butter two 6-cup souffle dishes. Set aside. Melt butter in heavy large skillet over medium heat. Add onions and saute until very soft, about 12 minutes. Mix in flour and stir 4 minutes. Transfer to bowl and cool to lukewarm. Add eggs to onion mixture and whisk to blend. Mix in corn, milk and salt. Season with pepper. Divide batter evenly between prepared dishes. Bake puddings until knife inserted into center of each comes out clean, about 1 hour. Spoon onto plates.