To make the batter for the crab, place the yeast, sugar, salt, beer, white balsamic vinegar, coriander and lime juice in a large bowl and whisk until smooth.
Add the flour and whisk until the batter is well combined. Leave to rest for an hour.
Preheat a deep fat dryer to 190C/370F, or until a cube of bread sizzles and turns golden-brown when dropped in the oil. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Dip the crabs in the batter and place in the deep fat fryer for 3-4 minutes turning two or three times, until golden-brown and crisp.
Carefully remove the crabs from the hot oil using a slotted spoon, place on a plate lined with kitchen paper and season with salt.
For the aioli, place the garlic and white wine in a pan and cook for a few minutes, then drain.
Place the egg yolks in a small food processor, add the vinegar, Dijon mustard and salt. Blend until smooth, then with the motor running, gradually add the oil until the mixture resembles mayonnaise. Add the saffron and garlic and blend to combine. Add lemon juice to taste.
For the watercress salad, place the watercress, mint and pea shoots in a bowl. Heat a small wok and add the oil. Once hot, add the chillies and cook for a couple of minutes.
To serve, place the deep fried crab on a board and place the leaves next to it. Top the crab with the fried chillies and place the aioli in a bowl.