For the vodka and tonic soft shell crab, preheat a deep fat fryer to 190C/370F. (CAUTION: do not leave unattended. Hot oil can be dangerous.)
Mix the yeast, salt and sugar in a bowl until well combined. Pour in the tonic water and whisk in the flour, vodka and vinegar. Set aside to ferment – it is ready to use when the mixture starts to bubble.
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 saffron aioli, place the garlic and white wine in a pan and cook for a few minutes. Drain and reserve the garlic.
Place the egg yolks in a food processor, add the vinegar, Dijon mustard and salt. Blend until smooth, then with the motor running, gradually add the oil in a slow trickle until the mixture resembles mayonnaise. Add the saffron and garlic and blend to combine. Add lemon juice to taste.
For the seasonal salad, place all the leaves in a large bowl and mix. Place the oil, vinegar and lemon juice in a small bowl and whisk. Pour over the salad and mix.
To serve, place the crab on serving plates with the salad next to it and the saffron aioli in a small dish. Scatter the spring onions over the crab.