Preheat a deep fat fryer to 190°C.
Combine yeast, salt, and sugar in a bowl.
Whisk in tonic water, flour, vodka, and vinegar then set aside to bubble.
Dip crabs in batter and fry for 3-4 minutes until golden.
Drain crabs on kitchen paper and season with salt.
Cook garlic in white wine for a few minutes then drain.
Blend egg yolks, vinegar, mustard, and salt in a food processor.
Stream in rapeseed oil gradually while blending to emulsify.
Add drained garlic, saffron water, and lemon juice then blend.
Whisk olive oil, vinegar, and lemon juice together for the salad dressing.
Toss salad leaves with the dressing in a large bowl.
Serve crab with salad, aioli, and a garnish of spring onions.