1. Peel the onions, but remove as little of the bottom of each onion as possible, as this will hold the onion together. First cut a cross in the onion without completely quartering it. Then make another 2-3 slits in each quarter section of the onion.
2. Season the flour with salt and pepper and beat the eggs and the milk together.
3. Carefully dip the onions in the flour, ensuring that the flour gets down into the slits. Shake off any surplus flour.
4. Now dip the onions in the egg mixture, ensuring they are well coated, before finally dipping them in the flour again.
5. Heat the oil in a deep pot. Carefully lower the onions into the oil, with the slits facing downwards. Turn after about 2 minutes. Deep-fry for another 7-8 minutes until the onions start to turn brown and crispy.
6. Remove the onions from the oil, allowing any surplus cooking oil to drain off. Place the deep-fried onions on paper towels and sprinkle with salt.
7. Melt the butter and stir in the flour. Add the milk a little at a time until you have a very thick white sauce. Cook for a few minutes. Grate the Extra Mature Cheddar cheese, and add to the sauce.
8. Let the cheese melt, and finally add the chipotle and whip with a hand blender to remove any lumps. Season to taste with salt and pepper. Serve immediately.