Cook the finely chopped shallots in the butter. Pour in the Noilly Prat and reduce to a syrupy consistency, then add the fish stock and reduce by half. Stir in the cream and bring to the boil, cook gently for 10 minutes. Sieve the mixture and keep warm.
Blanch the ginger in boiling water and refresh under cold water. Melt the butter, add the rhubarb with enough water to cover it, and cook for about 5 minutes or until soft. Remove the rhubarb and keep in a warm place. Reduce the rhubarb cooking liquid to almost nothing, and stir in the velouté sauce. Reheat just before serving.
Heat a non-stick pan, add the 4 pieces of salmon and lightly season with salt and freshly ground white pepper. Cook lightly on either side–leave it slightly pink in the middle. Put the velouté sauce on the plates, place the salmon on top, decorate with the rhubarb and ginger. Serve at once.
Julienne of ginger can be blanched and preserved in dry sherry for use when needed.