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Separate one of the three eggs for the asparagus. Put the white in a bowl with the remaining two eggs, beat with a fork and set aside until needed. Now, make the baconnaise. Chop the bacon as finely as possible. Heat the oil in a frying pan, add the bacon and stir over a low heat for 15 mins, so it ends up sizzling in its own fat and becomes brown and crisp. Sit a metal sieve over a jug and tip the bacon into the sieve – you need about 200ml of fat in total, so top up the bacon fat with extra oil as necessary. Leave to cool for 10 mins.
Tip the egg, egg yolk and mustard into a bowl, whisk to combine, then slowly add the bacon fat and oil mixture – first a drop at a time, then gradually quicker when it starts to come together. (You can also make this in a mini chopper, by blitzing the egg and mustard then slowly adding the oil with the blade running.) Once you have a thick mayonnaise, add the vinegar and chopped bacon, and season to taste. Can be made up to three days ahead and kept in the fridge.
For the asparagus, snap off or trim the woody ends (save for making stock or soup). Get out three shallow dishes and tip the flour into one, the reserved beaten eggs into another, and the parmesan and breadcrumbs into the third. Dip the asparagus in the flour, then the egg, then the cheesy breadcrumbs, and put on a plate. Can be prepared the day before, covered and kept in the fridge.
Heat oven to 220C/200C fan/ gas 7. Drizzle the oil over a baking tray (a sturdy Swiss roll tin is ideal) and heat in the oven. Once the oil is hot, carefully lay the asparagus spears in it, then turn them. Make sure they are in one layer, then roast for 20 mins, turning halfway through, until the crumbs have browned to a crisp coating. Leave until just cool enough to pick up, then serve with the baconnaise for dipping.