Grill or bake the aubergines until the skin is charred. Clean them straight away whilst they are still hot, wearing gloves so you don't burn your fingers
Drain the flesh of the aubergines in a sieve, over a bowl, for at least two hours, to drain the bitter liquid inside.
Finely dice a small onion
Chop the flesh of the aubergines with a stainless steel knife until it is fully mashed.
Add the chopped aubergines into a bowl and mix with the onions, mayo, and salt.
Serve cold, on slices of bread.