Trim any white sinew or fat from livers. Rinse in a colander with cold water. Drain then pat dry. Heat 50g of the butter in a large non-stick frying pan over a medium heat. Add eschalot, garlic and thyme. Cook, stirring, for 1 minute or until soft.
Add livers and cook for 5 minutes or until lightly golden all over but still pink on the inside. Add brandy and zest. Cook for 20 seconds. Pour mixture into a bowl. Let cool.
Put in a food processor and process until pureed. With the motor running, gradually add remaining butter and crème fraîche through the food chute. Season to taste and process until combined.
Transfer mixture to a fine sieve over a bowl and push through with a spatula. Discard solids left in sieve. Spoon mixture into small cups or moulds and smooth the surface, leaving ½ cm for butter layer. Pour clarified butterfat over to cover and garnish with a small sprig of thyme. Refrigerate overnight. Serve with bread. Pâté will keep, covered, in the fridge for up to 4 days.