For the brill, place the shallot, thyme, parsley, garlic and wine into a large deep frying pan and bring to the boil.
Turn down the heat to a gentle simmer. Add the brill and poach for 5-6 minutes, or until just cooked. Remove from the pan, set aside and keep warm.
Strain the cooking liqueur into a separate pan and bring to the boil. Boil rapidly to reduce the liquid volume by about two thirds.
Season the sauce with salt and freshly ground black pepper, then whisk in the cold butter. Do not bring the sauce to the boil again.
For the colcannon, place the cream and butter into a large bowl with the warm mashed potato and mix well.
Add the cabbage and spring onions and fold together. Season, to taste, with salt and freshly ground black pepper.
To serve, place a spoonful of colcannon onto four plates. Place a piece of brill onto each, spoon over some of the sauce and finish with a little freshly grated fresh nutmeg.