Blend four of the pieces of lemon sole and all of the offcuts in a food processor with 75ml/2¾fl oz of the cream, until the mixture has been reduced to a fine paste. Season with salt and freshly ground black pepper and pulse once more until smooth, then transfer the mixture to a piping bag.
Lay 4 pieces of the lemon sole onto separate sheets of aluminium foil and season all over with salt and freshly ground black pepper.
Pipe a layer of the fish and cream mixture all over each piece of lemon sole. Top each with another piece of lemon sole and top that with another layer of the fish and cream mixture. Finish each with a third piece of lemon sole. You should end up with four stacks of fish, each containing 3 rectangles of lemon sole and 2 layers of filling.
Wrap each lemon sole stack in its sheet of foil, then chill in the fridge until ready to cook.
Meanwhile, add half of the cauliflower florets to a saucepan and pour over the remaining cream. Bring to the boil, then reduce the heat and simmer for 4-5 minutes, or until the cauliflower florets are tender.
Transfer the cauliflower and cream to a clean food processor and blend to a fine purée. Season, to taste, with salt and freshly ground black pepper. Set aside until needed.
Bring a pan of salted water to the boil and cook the remaining cauliflower florets for 2-3 minutes, or until just tender. Drain well.
Finely grate the remaining raw cauliflower into a bowl, then grate over the boiled egg and stir in the chives until well combined.
In a separate bowl, whisk the white balsamic vinegar and olive oil together until well combined. Set aside.
Suspend a steamer over a pan of simmering water. Add the sole parcels to the steaming basket, cover and steam for 6-8 minutes, or until just cooked through. Remove from the steamer and, when cool enough to handle, carefully unwrap and discard the foil,
Just before serving, spoon two-thirds of the dressing over the cauliflower and egg salad and mix to coat. Season with salt and freshly ground black pepper.
Mix the remaining dressing with the drained cauliflower florets and cooked langoustines and stir gently to coat.
To serve, drizzle a line of the cauliflower and cream purée across the centre of each plate. Place one lemon sole stack on top of each line, in the centre. Spoon a portion of the cauliflower and egg mixture on one side, and the cauliflower and langoustines on the other side. Garnish with fennel fronds, if desired.