1. Preheat the oven to 140 ̊C, gas mark 1. Melt 20g butter in a frying pan and fry the livers for 1-2 minutes on each side, until just browned. Remove from the pan and set aside.
2. Gently fry the shallot in another 20g butter in the pan with a pinch of salt for 5 minutes, until soft but not coloured. Add the garlic, thyme and bay; cook for 1 minute. Add the sauternes and bubble for 2-3 minutes, until slightly reduced, scraping the pan. Take off the heat, discard the bay and tip everything into a food processor with the livers, nutmeg, eggs and salt.
3. Gently warm the remaining 180g butter with the cream in a small pan. Blend the liver mixture and slowly pour in the buttery mixture in 2-3 additions, blending to a smooth liquid. Pass through a fine sieve into a wide jug, pressing it with a wooden spoon.
4. Divide between 8 small ramekins, leaving a 0.5cm gap at the top of each. Put them in a large, deep roasting tray and pour in enough just-boiled water to reach 2/3 up the side of each ramekin. Cover with foil and bake for 30-40 minutes, testing after 25 minutes with a digital thermometer. Once they reach 70 ̊C in the middle they are ready and should be just set. Transfer the ramekins to a wire rack to cool completely; cover and chill overnight.
5. For the jelly, bring the sauternes to a simmer in a small pan; take off the heat and cool slightly. Soak the gelatine in cold water for 5 minutes. Squeeze out the water, then stir into the wine until dissolved; pour into a small bowl and cool. Set this bowl in another bowl of ice; stir until the jelly thickens but is still pourable.
6. Smooth any cracks on the surface of the parfaits and top each with 2 thyme sprigs. Pour over the jelly until evenly covered. Chill for 1-2 hours, until set. Take out of the fridge 15 minutes before serving. The parfaits can be stored in the fridge for up to 24 hours.