Prepare the chicken livers: Remove any gristle and bile duct. Chop and combine with the pork neck.
Peel and chop the onions into rounds, keeping some aside for decoration.
Place the chicken livers, neck of pork, eggs, onions, thyme, bay leaf, ground Espelette pepper in a food processor. Season, add the Marsala, and process.
Preheat the oven to 170°C | 325F | gas 3.
Transfer the mixture to a terrine, press down well and cover. Place the terrine in a dish filled two-thirds with water.
Transfer to the oven and bake for 1 hr 30 minutes.
Remove the terrine from the oven and the bain-marie, leave to cool and then chill.
When ready to serve, decorate with chopped onion and an Espelette pepper.