In a pan melt 1 Tbsp of the butter over medium heat.
Add the onion to the melted butter and saute until soft.
Add the garlic and gently cook through until fragrant, about 1 minute.
Add the chicken livers, 1 tablespoon of the peppercorns, thyme, rosemary, salt, and pepper. Cook through until the livers are browned on the outside and still slightly pink in the middle, stirring regularly, about 5 minutes.
Add the brandy or cognac and cook until most of the liquid has evaporated and the livers are cooked through.
Take off the heat and allow the mix to start to cool.
Add the mixture to a blender or food processor with the creme fraiche or cream if using or duck fat and blend on a medium speed for about 2 minutes or until a smooth consistency.
Then add in the remaining 1 tablespoon of peppercorns and gently fold through the mix. Taste and adjust the seasoning, to your liking.
Place the pate into individual ramekins, small holds or containers. Cover with extra melted butter (if using).
Cool and cover to place in the fridge until firm, approximately 5 hours.