1: First remove the tough core from the fennel and cabbages. Shred them finely either with a sharp knife or with a mandolin, along with the celeriac, carrots, beetroot and onion. Place them all in a large mixing bowl. Add the flaky sea salt and mix thoroughly. Leave to soften for 20 minutes.
2: Meanwhile, make the dressing. Place the egg yolks, mustard, vinegar, sugar, lemon juice, garlic and anchovies in a food processor and blend until smooth. With the motor running, slowly pour in the oil through the feed tube until the mayonnaise is smooth and emulsified. Season to taste with salt and cayenne pepper then pass the mayonnaise through a sieve to make it really smooth. This can be made ahead of time and stored, sealed in the fridge, for up to a week.
3: Place the vegetables in a colander and rinse under cold, running water for 2-3 minutes, then leave to drain. Place them in a clean tea towel and squeeze out the excess moisture. Put them into a clean mixing bowl. Add the lemon zest, fennel seeds, herbs and check the seasoning.
4: Fold in enough mayonnaise to coat generously. You may not need it all. Mix together and serve.