Reduce port and calvados at a quick simmer until syrupy (approx 40 minutes)
To make the parfait - heat butter, fresh thyme and garlic, cook gently for 10 minutes or until tender and remove from heat and allow to cool at least 5 minutes. Remove thyme sprigs.
When the port is reduced then place the livers into a liquidizer, together with lightly beaten eggs and quite warm garlic and butter and salt petre - liquidize until fine and smooth.
Now add the reduced port and calvados and truffle oil, add milled pepper and salt slightly over season to taste.
Taste check. Pass through a fine sieve into a clean container (the mix should be quite warm or it will difficult and lots wasted when passed through the sieve).
Fill terrines, cover with butter paper and a lid, poach in a waterbath at 275F/135°C for approx 45-55 minutes or until firm but wobbly.
Allow to cool, then cover and refrigerate to become firm. When firm turnout onto a board.
Thyme butter: simply beat soft butter and fresh thyme leaves together until butter is light and white.
Using a palette knife, smooth a 2-3mm think layer all over the outside of the unmoulded terrines, refrigerate then turnover and cover the one remainin unbuttered side. Refrigerate then cover with cling film until needed.