Slice the onions crosswise and separate into rings. Combine milk, eggs, and salt to taste in mixing bowl. Soak the onions in the mixture about 30 minutes. Place pancake batter in a shallow bowl. Heat oil for frying in skillet to 375 degrees. Remove the onion rings from milk mixture, dip in pancake mix and place in hot oil. Fry rings until golden brown and drain on paper towels. Pack fried onion rings solidly, but loosely, without pressing, into an 8-by 4-inch loaf pan. Bake at 400 degrees for 10 to 15 minutes. Turn out onto serving plate.